List of inconsistencies in the Halo series

"Science Team Leader"

- ONI Commander "So, um, how come do you figure stuff looks different sometimes? Like guns, or the Arbiter? Like do you remember being more purpler? I do! Eh, maybe it's just my eyes getting smart, but I swear sometimes it's like a whole spaceship is different and nobody says anything. I mean was the Gravemind always so much scary? I dunno, he was like a big puppet, big flabby thing. Eh, maybe it's just me that notices stuff."

- Dimkee Hotay, noting cosmetic retcons in the Halo universe. This list is compiled to show the various discrepancies spotted in the Halo universe. Inconsistencies on the list are divided into two types: internal and external. Internal inconsistencies refer to discrepancies which occur within a single source, while external inconsistencies are conflicts between two or more sources.

It is often difficult to decide which resource is "superior" to another, so conflicts are mostly listed in a chronological order. Likewise, it can rarely be conclusively determined whether a conflict is the result of an oversight on part of the author or editor(s) or an intentional retcon, unless this is specifically confirmed by the developers of the Halo franchise; such cases are noted accordingly. For more information, see here. There have been a number of cases in which an apparent inconsistency arises within an individual piece of media, only to receive a canonical workaround in another source; an example of this is the shared designation "Type-47 Scarab" for the two different Scarab models appearing in Halo 2 and Halo 3, something that was eventually clarified as "a UNSC administration quirk". For inconsistencies that have since been resolved by other Halo media, see List of rectified inconsistencies in the Halo series.

Many inconsistencies on this page are provided possible explanations, although it should be noted that these are only unofficial theories unless otherwise stated, and may not reflect the franchise developers' stance on the matters in question. If you think you can explain an inconsistency, do so here, on this article's talk page.

Inconsistencies
In instances in which two or more works have been developed concurrently and released within a short span of time of one another (e.g. games and their marketing material), the "primary" work takes precedence on this list even if released marginally later than the "secondary" one. For example, conflicting information in Halo: The Fall of Reach is said to contradict Halo: Combat Evolved, even though the novel was released slightly earlier than the game. Conflicts which are persistent throughout multiple sources are listed in the "Several sources" section.

Halo: The Fall of Reach

 * Internal
 * The Eridanus II space dock is erroneously stated to be located in the Epsilon Eridani system in the chapter heading for Chapter 10. Throughout the rest of the book, Eridanus II is correctly referenced as being located in the similarly named Eridanus system.


 * When Dr. Halsey and the Spartans are on a Pelican leaving the Damascus Testing Facility, Halsey tries to adjust her glasses but can't due to her space helmet. Despite this she is later said to tap her lip in thought.


 * The time stamp for Chapter 23 is labeled "0500 hours, July 18, 2552", even though the events portrayed take place after the preceding chapters which occurred over the evening of July 18; the previous chapter begins at 2010 hours that day.
 * It is possible that while Chapters 18-22 are labeled as occurring on July 18, they are supposed to take place on July 17. The time stamps suggest a day-long pause between Chapters 17 and 18, and although this can be justified by Admiral Stanforth's Battle Group Leviathan taking more than several hours to reach the Sigma Octanus system, the description of the battle on the surface suggests the events occurred during the same day as the initial space battle. Alternatively, the date in Chapter 23's heading could simply be a mistake, with the intended date being July 19. This is corroborated by the second Data Drop, in which Stanforth sends a message to Admiral Parangosky in the immediate aftermath of the Battle of Sigma Octanus IV at 2300 hours on July 18, 2552.


 * When John-117 reflects on his life in August 2552, he notes that the Spartan-IIs were conscripted "twenty-five years ago". The candidates were actually kidnapped in 2517, nearly 35 years prior.


 * John-117 internally notes that he had "overheard" Dr. Halsey mention Chief Mendez departed to train a new group of Spartans. Earlier in the novel, Halsey explicitly tells John and the other Spartan-IIs of Mendez's future role.


 * On August 30, Cortana mentions that her test with John-117 and the Mark V MJOLNIR occurred "this morning", even though the test took place a day earlier.


 * Chief Petty Officer McRobb states that his posting on Fermion was part of the UNSC's new policy to staff Remote Scanning Outposts with their most competent personnel—a policy that was put into effect following the Battle of Sigma Octanus IV just over six weeks earlier. Despite this, he notes that he had spent three months preparing his crew for the new assignment.


 * External


 * Grunts are said to be about a meter tall. Subsequent material portrays them as roughly 1.5 meters tall.


 * John-117 notes that he "had seen a disarmed Jackal fight hand to hand rather than pick up a nearby human assault rifle" as an example of the Covenant's abhorrence of human weaponry. While this may apply to most of the Covenant species, such behavior is rather out of character for the Kig-Yar in light of their gameplay tendency to flee from melee combat. In addition, later backstory has established the Kig-Yar as opportunistic mercenaries rather than faithful adherents of the Covenant religion, making the described behavior seem even more out of place. Additionally, in Halo: Reach Covenant Elites and Grunts will occasionally use human weapons, such as M247 and M41 turrets encountered on the battlefield (though like all NPCs they cannot pick up dropped weapons). Furthermore, in a letter to Prophet of Truth written by Thel 'Vadamee, the Sangheili encourages use of human weapons if necessity requires it.


 * Covenant plasma pistols are said to have barrels in one description, even though the weapons do not possess barrels of any sort as the plasma projectiles are generated between the pistol's two "claws".


 * It is stated that the Hunters' assault cannons "seemed almost as powerful as the stationary plasma cannons the Jackals used.". In the games, the Hunters' weapons are considerably more powerful than the Covenant's stationary turrets, which are operated predominantly by Grunts and Elites.


 * When the Master Chief kills Elites and Jackals aboard Gamma Station, the aliens are said to bleed blue and green blood, respectively. Both species' blood is actually purple or purple-blue in the Sangheili's case.


 * The novel repeatedly describes slipspace ruptures as being green. Although no slipspace phenomena had been shown in visual media at the time of the novel's writing, all subsequent media has depicted slipspace ruptures as blue; the effects associated with slipspace-based teleportation are most often depicted as yellow or orange.


 * In Halo: The Fall of Reach, Aki Hikowa and Ellen Dowski are female officers of the Pillar of Autumn. However, on the level The Pillar of Autumn, the bridge has no female members.
 * This may imply that, like modern navy ships, the Autumn has rotating shifts. The obvious Doylist explanation is that no female crew members were modeled.


 * William Lovell's eyes are stated to be green in Halo: The Fall of Reach, but in Halo: Combat Evolved, the Autumn's crew has no green-eyed members.
 * This is likely a result of game engine limitations, or due to rotating shifts, Lovell was simply not present on the bridge at the time.


 * In Halo: The Fall of Reach, the description of the Pillar of Autumn is considerably different from its Halo: Combat Evolved incarnation. The bridge is described as having a command chair and a curved viewport; in Halo: Combat Evolved, this chair is absent and the window consists of several flat sections. The novel also describes the bridge as being extremely cramped, with only a meter of space between the command chair and the other stations, while in the game, the bridge is clearly more spacious. According to the novel, there is also an elevator leading directly from the engine room to the bridge. In the game, the engineering and the bridge are on the same level, and there are no doors which may belong to an elevator adjoining the bridge. In addition, the engine room is described as being "hexagonal", while in the game, it consists of two vaguely rectangular chambers with the engine core in the middle. In the Combat Evolved level The Maw, it is stated that the Pillar of Autumn has four fusion reactors, each of which is destroyed by the player; in The Fall of Reach, the ship is also said to have a single main reactor nestled within two smaller reactor rings. The ship is also described as having rotating centrifuges to generate artificial gravity; no rotating sections are present in the game, unless they are located within the hull.


 * In the Tor 2010 reprint of The Fall of Reach, Halsey's comment said in 2552 about Elites being a new species is edited, to reflect retcons that had them deployed since the beginning of the war. However, later on she states that "ONI hypothesizes at least two additional castes [which include] a warrior capable of commanding ground forces and possibly piloting their ships..." In the original 2001 print, this statement referred to Elites, but can't in the reprint due to them not being merely theorized anymore. It is possible Halsey may be referring to Brutes, but the Brutes too have been retconned to have been deployed at the war's start, with both Halsey's journal and the following reprint of First Strike confirming that they were encountered well before 2552.


 * In Halo: The Fall of Reach, when Captain Keyes awakens from cryo, Cortana informs him that the capacitors of the Pillar of Autumn's MAC gun are depolarized and the gun cannot fire, yet the gun is apparently used, and the loss of fire control is treated as a significant development in Halo: Combat Evolved's opening cutscene.
 * It is possible that the crew managed to get the gun working again before the battle.


 * The ONI Directorate Memorandum Interrogation Findings log included in the Adjunct section of the 2010 edition of Halo: The Fall of Reach refers to Preston Cole as a fleet admiral. Though there is a conflict over Cole's rank between Halo Wars: Genesis and The Impossible Life and Death of Preston J. Cole (see here), no other source has referred to him as a fleet admiral.


 * In order to destroy the RSO Fermion, Chief Petty Officer McRobb saturated the station's fusion reactor chamber with deuterium. However, basic physics would dictate that such a method would not work. In fact, it is impossible to cause a fusion reactor to explode in real life by design.

Halo: Combat Evolved

 * Internal
 * The main view screen on the labels the yet unidentified ring as "Halo". The name of the ring is not discovered until the level The Truth and Reconciliation. This mistake is repeated in Halo: Combat Evolved Anniversary.
 * Cortana says she cannot begin to calculate Halo's pulse range just after 343 Guilty Spark finishes telling her it has a radius of 25,000 light years.
 * This can be accounted for by Cortana's inherent distrust of Guilty Spark's motives. Additionally, since Cortana is an AI with an insatiable urge to know everything she can, she may have tried to calculate the range herself regardless of whatever 343 Guilty Spark had told her.
 * Almost every Pelican dropship bears the marking "E419", on its side, despite the fact that each Pelican has a different serial number.
 * There is no canon explanation. This is due to only two Pelican textures, V933 and E419, being used to represent every Pelican in the game.
 * During the Warthog Run portion of The Maw, the player has to travel a direct distance of over three kilometers atop the Pillar of Autumn to reach the Longsword fighter, but the Autumn is only 1.17 kilometers long. The Longsword's launch bay is also at the end of the Warthog run. The front or rear of a ship is an unlikely place to store a launch bay, which implies that the Master Chief traveled from side to side, further straining the realism of the sequence.
 * During the level Assault on the Control Room, Staff Sergeant Johnson can be seen with the Master Chief at the time he was really with Captain Keyes searching for the Covenant's "weapon cache"; even though the Captain has been out of reach since The Silent Cartographer.
 * This is a result of Bungie reusing the "Johnson" NPC instead of creating another sergeant model. The same can be said for Gunnery Sergeant Stacker, who was treated as a generic NPC until Halo 4, when he was finally explicitly identified in gameplay.
 * In 343 Guilty Spark a body collapses on the Master Chief in the room where the Flood is introduced. It is unclear as to why this Marine was not infected when the Flood overran the personnel in the room.
 * From an out-of-universe perspective, it's possible the Flood were not meant to infect dead bodies, but only take live hosts during the writing of Combat Evolved. The Paranoid Marine may mention that he escaped the Flood by playing dead, a tactic that would not work after Halo 3, where the Flood are witnessed infecting dead bodies.

Halo: Combat Evolved manual

 * External
 * The Halo: Combat Evolved manual states that the Harvest incident took place in 2520. Halo: The Fall of Reach and all subsequent media unanimously place the attack in 2525.
 * The manual states that Captain Keyes has served in the UNSC since 2526, though The Fall of Reach clearly states that he had recently graduated from OCS in 2517.
 * According to the manual, the Covenant attacked Reach two days before the Spartans' mission to capture a Prophet was to begin. This is contradicted in Halo: The Fall of Reach and First Strike, in both of which the Pillar of Autumn is already departing for the mission when the Covenant attack.
 * The manual refers to the as a colony ship. The ship is said to be a frigate in Halo: The Fall of Reach.

Halo: The Flood

 * External
 * In Halo: The Fall of Reach, Lieutenants Hall and Dominique are introduced as members of the command crew of the Pillar of Autumn, but are absent in Halo: The Flood when the ship arrives at Installation 04.


 * On page 3 of Halo: The Flood, Thom Shephard tells Sam Marcus that they are resuscitating John-117 before the Pillar of Autumn exits slipspace. However, in Halo: Combat Evolved Captain Keyes orders that John-117 be taken out of cryo after the Autumn is seen drifting in space and is preparing to be overrun by the Covenant.


 * In Halo: The Flood, the presence of the Covenant at Installation 04 is considered unrelated to the arrival of the Pillar of Autumn; the Covenant are surprised by the arrival of the human ship and act as if it ended up in the system by either following one of their ships, or by chance. However, Halo: Combat Evolved, Halo 2 and the Covenant broadcast log featured in the Adjunct section in the 2010 reissue on The Flood, state that the Covenant found the ring specifically by following the Autumn's slipspace jump from Reach, and arrived at the system in advance, waiting for the Autumn on the far side of Threshold.


 * In Halo: The Flood, Cortana identifies Installation 04 as "Halo" when escaping the Pillar of Autumn, but in Halo: Combat Evolved, it is not identified by this name until the level Truth and Reconciliation, when Captain Keyes mentions overhearing the name from his Covenant captors.


 * According to Halo: The Flood, there was an ocean at the bottom of the desert plateau the Truth and Reconciliation was holding position on. However, in both Halo: Combat Evolved and Halo: Combat Evolved Anniversary, there is only solid ground below the plateau.


 * In the Halo: Combat Evolved level Halo, Cortana mentions that the survivors rescued by John-117 would be transported to the "command shuttle". The command shuttle is not mentioned in Halo: The Flood, where Alpha Base serves as the main command post for UNSC forces.


 * In Halo: Combat Evolved, Cortana accesses Installation 04's Control Center by having the Master Chief remove her memory chip from his helmet and place it in the console. In Halo: The Flood, she broadcasts herself into the system using the suit's transmitter.


 * There are several differences between Halo: The Flood and the Halo: Combat Evolved level The Maw in the encounter at the final service elevator on the Pillar of Autumn. In Halo: The Flood, Zuka 'Zamamee confronts John-117 by using a Shade turret, accompanied by several Grunts. Cortana takes control of the elevator and causes it to descend, allowing John-117 to drop in a pair of grenades and take out the Covenant. In the game, Cortana does not move the elevator and there are two Special Operations Elites and no Shade turret aboard.


 * In Halo: The Flood, many of the Marines John-117 fought alongside were female, despite no female Marines being in Halo: Combat Evolved at all. The Doylist explanation for this could easily be that there were only male marines modeled and voice-acted, and we should not take it as canon that there were no female marines on Installation 04.


 * In Halo: The Flood, Sergeant Stacker is not mentioned at any point, despite him being present on several occasions in the game. He is replaced during the raid on the Truth and Reconciliation by Sergeant Parker, and for the raid on the Silent Cartographer by Gunnery Sergeant Waller. One place where he might make an appearance is when the Chief rescued a crashed Marine squad with an unnamed Sergeant, where Stacker is normally found in the game.


 * Throughout Halo: The Flood, the Master Chief's or other characters' weapon loadouts at a given situation occasionally differ from those in the game. Stocks of ammo left behind by dead marines are not mentioned either.
 * In Chapter 4, during the raid on the Truth and Reconciliation, the novel illustrates that John ran out of ammo for his MA5B Assault Rifle, switching to an M6D pistol; in the game, there are no pistols on that level at all.
 * Also in Chapter 4, it is stated that "the Spartan was carrying a full combat load of ammo, grenades, and other gear, plus two magazines for the M19 launchers". In the game, the Master Chief was not carrying a rocket launcher nor any magazines for it at the time.
 * The novel consistently describes Marines wielding rocket launchers; no marines are ever seen wielding rocket launchers in the game.
 * This is due to in-game constraints, as is the inability for marines to drive Warthogs.


 * As revealed in later sources, the Covenant has revered Forerunner AIs as "Oracles" for a long time, but in Halo: The Flood, 343 Guilty Spark was regarded as an enemy by the Sangheili.
 * This is probably because the fiction regarding the Covenant's beliefs had not yet been cemented by the time The Flood was written.


 * Major Silva states intimate knowledge of the Spartan II program, specifically the child abductions, despite such details being strictly confidential. A Major in the ODST branch would certainly not have access to such information, nor toss it out so casually for no better purpose than to insult a Spartan.

Halo: First Strike
In Chapter 33, it is said that Will and Linda went out to secure the area. It then says that the Master Chief climbed up to where Fred and Linda perched. Immediately after it says that Fred and Grace disembarked the dropship implying that Fred was still in the dropship and it is presumed that it was meant to say Will and Linda.
 * Internal


 * External


 * Prior to colliding in the launch bay of Ascendant Justice, the Longsword is going at a speed of 300 m/s. This is equivalent to 1080 km/h (671 mph) and a sudden stop at that speed would kill the occupants immediately because of whiplash.
 * This is likely a typo with the correct value being 30 m/s. Strangely, this has not been corrected in the Definitive Edition.


 * John-117 notes that Ascendant Justice was the largest Covenant ship he had ever seen with its length of three kilometers. However, several staple Covenant ship types the Master Chief had encountered over his career, such as the, are significantly larger than the Ascendant Justice ' s described size.
 * This is likely because the larger Covenant ship classes such as the CAS had yet to be introduced at the time of the novel's writing, although the error remains in the 2010 reissue.


 * In Halo: Combat Evolved, the Master Chief throws Private Jenkins' recorder chip away, but he still has it in First Strike. This could be explained by the Chief's suit automatically making a copy of Jenkins' recording as a possible means of gathering intelligence, although this is only a theory.


 * It is stated in Halo: First Strike that Dr. Halsey always referred to John by name, and never by rank or serial number. However, in Halo: The Fall of Reach, she called him "Master Chief" repeatedly.


 * Frederic-104 fires three shots from a Wraith's plasma mortar which are powerful enough to reduce at least two Scarabs as well as nearby Covenant mining equipment to "piles of half-melted junk". While the Scarabs were not named as such in the original edition (being only referred to as "insectlike diggers" and "giant insectlike machines"), the 2010 reissue's identification of the vehicles raises an inconsistency regarding their durability; in the games, Scarabs require sustained and concentrated fire to their weak points to take down, making the Wraith's mortar in the novel disproportionately powerful.


 * The city of Côte d'Azur is repeatedly referenced as if it were a planet; this mistake is repeated in Halo: Ghosts of Onyx. Although First Strike and Ghosts of Onyx clearly refer to the Côte d'Azur described in The Fall of Reach, this confusion may have given rise to the introduction of the separate planet named Cote d'Azure in later media.


 * During Chapter 33 of Halo: The Fall of Reach, many Covenant ships are destroyed, but not before they can let loose their plasma torpedoes which then destroy UNSC orbital defense platforms. However, during a space battle in Halo: First Strike, plasma en route to a target merely dissipates as the originating ship and its magnetic controls are destroyed.
 * It is possible that the magnetic controls were not destroyed in the former instance, allowing the plasma to continue to its target.


 * The Prophet of Truth's description differs considerably from his visual appearances, presumably because the Prophets' appearance had not yet been decided upon when the novel was written. While written from an ostensibly Covenant point of view, Truth is described as an "it" instead of a he. Truth is also said to have sensor and respiratory apparatus like insect antennae in his headpiece as well as protruding eyes and a snout, the rest of his face remaining obscured. Strangely, the description remains unaltered in the 2010 Definitive Edition.


 * The interrogation transcript featured in the Adjunct section of the 2010 edition of Halo: First Strike continuously refers to Frederic-104 as a lieutenant by the start of the Battle of Earth. In Halo: Ghosts of Onyx, Frederic-104 is not promoted to the rank of Lieutenant, Junior Grade until the end of the Onyx Conflict.

Halo 2

 * Internal
 * In the cutscene Another Day at the Beach, the UNSC forces that land near Hotel Zanzibar wear ODST armor, reflecting the analogous scene from the Halo 2 E3 demo. When the Marines are encountered at the hotel during the level Outskirts, they wear standard Marine BDUs. Also, the location of the crashed Pelican does not match its position in game.
 * This is because Another Day at the Beach was cut from the game before release. The Marines from the crashed Pelican were likely switched to regular Marines later in the level's development.
 * In the level Delta Halo, seven dead ODSTs are strewn about quite far from the landing zone. However, In Amber Clad dropped only eleven SOEIVs in the opening cinematic. The Master Chief, the three ODSTs who land near him, the three killed near the intended landing zone, and the seven ODSTs means that fourteen SOEIVs should have been deployed. This is probably a deliberate reference to the number seven: 14=7x2.

Halo: Ghosts of Onyx

 * Internal
 * Kurt Ambrose's rank was apparently lieutenant commander in 2545, as said in the prologue. However, he was still referred to as a lieutenant by 2551 later in the story. In Chapter 13, he is referred to as a lieutenant and then lieutenant commander several lines later.


 * CPO Mendez remarks that Tom-B292 and Lucy-B091 are ten years old in Chapter 9, which is set in August 2541. However, it is previously established that both of them are twelve during Operation: TORPEDO in July 2545, meaning that they would have been eight years old in 2541. It is possible that Mendez misspoke as a result of not remembering the specific age of every individual Spartan due to their large numbers and the age differences between them.


 * In November 2552, Kurt states that the previous Zone 67 AI sent him a message via a slipspace probe "years ago", even though the incident to which he refers took place in February 2551, less than two years earlier. It is likely that he simply misspoke.


 * Kurt states that the Onyx Sentinels first appeared on the morning of September 21, 2552, with Dr. Halsey noting that this date coincides with the "activation" of Installation 04. However, earlier in the novel the Sentinels are described as appearing on the morning of October 31, unless they had been previously active in Zone 67 and Kurt learned this after the October 31 attack from Endless Summer's transmissions. It should also be noted that Installation 04 was never actually activated; although John-117 inserted the Activation Index to the Core, Cortana prevented the activation sequence from commencing. However, it can be assumed that this, or the related events on Installation 04, were enough to alert Onyx's Sentinels; they could not have been roused by the arming of the Halo Array from Installation 05, as this did not occur until November 3, although the Halos' arming is mentioned as having started the countdown to the closing of Onyx's shield world portal.


 * Ash-G099 is once addressed as a private. Although the novel does not explicitly identify Gamma Company's branch of service, they (like the rest of the Spartan-IIIs) are heavily implied to be Navy (this is later confirmed in Halo: Glasslands). The rank of private does not exist in the Navy and would be atypically low for Ash given his role as Team Saber's leader.


 * The narrator mentions the "ancient feud" between the Sangheili and the Jiralhanae at the time of the Great Schism. As it was later established, the Jiralhanae were discovered by the Covenant in 2492, which would hardly make the two species' feud "ancient".


 * External
 * It is stated that the MJOLNIR Mark IV armor has an AI interface port in a chapter set in 2531. The AI interface was not added to the Mjolnir system until the final model of the Mark V in 2552.


 * The frigate is erroneously referred to as a destroyer.


 * In Halo: First Strike, Dr. Halsey puts four submachine guns in a bag. In Halo: Ghosts of Onyx, Kelly finds the same weapons, but they are four MA5B assault rifles instead.


 * In Halo: Ghosts of Onyx, Kurt Ambrose remarks that some of the Alpha Company candidates were orphaned at Jericho VII. His speech takes place on December 12, 2531, yet Jericho VII was not glassed until February 2535.
 * While this is most likely to be a simple oversight, it is possible that the candidates from Jericho VII were orphaned in a yet-unseen engagement that preceded the Covenant attack of 2535, as the background of the Covenant invasion of Jericho VII is not elaborated upon in The Fall of Reach. For example, the events that occurred may have been similar to how the Covenant initially invaded Arcadia in 2531 but only arrived to glass the planet eighteen years later.


 * Dr. Halsey notes that Kurt stands "nearly two and a half meters" tall in his SPI armor. This is suspect, as Kurt is never remarked as being unusually tall among the Spartan-IIs. Samuel-034, by far the tallest of the Spartan-IIs, stood at 238.8 centimeters in his Mjolnir armor, while Jorge-052 was noted to be unusually tall for a Spartan-II at his 223.5 centimeters in height.


 * On page 129 of Halo: Ghosts of Onyx, Franklin Mendez is mentioned to be "pushing sixty [years old]" in 2552, which implies that his birthdate is close to or after 2493; he is previously mentioned as having "aged well" in 2531. However, this would give him a maximum age of 24 when he started training the Spartan-IIs, which is unlikely given his description in Halo: The Fall of Reach as a grizzled veteran instructor who had seen much combat, as well as his high rank of Chief Petty Officer, as of 2517. Additionally, because combat-oriented UNSC military personnel typically spend significant spans of time in cryosleep Mendez's biological age would likely be even less than his nominal one. Mendez's Halo Waypoint biography establishes his date of birth as March 24, 2492, making him 60 years old at the time.

Halo 3

 * Internal
 * Every Longsword fighter bears the marking 7-89 on its side, despite each Longsword canonically having a different serial number. This is the result of reusing the same model for all Longswords in the game.
 * In the ending cutscene of the level The Storm, all three UNSC frigates have the same serial number and all are labeled "Forward Unto Dawn". This is also obviously the result of reusing the same model.
 * In the ending cutscene of the level Halo, the Arbiter is shown sitting at the bridge's helm after leaving the hangar. After the Dawn is cut in half by the portal, the Arbiter arrives on Earth in the front half of the ship, yet the bridge remains attached to the back half of the ship. Presumably the Arbiter moved toward the fore end just before the ship was bisected. However, the cutscene appears to occur in real time; thus, he would have had mere seconds to descend roughly two decks from the bridge to the main hull, after which he would have to move forward at least fifty meters to avoid being caught in the aft section.

Halo: Contact Harvest

 * External
 * Halo: The Fall of Reach states that Harvest has a population of three million. However, in Halo: Contact Harvest, it is stated to have a little over 300,000. The figure presented in Contact Harvest has been ignored in later media, and the population is listed as three million in Halo: Fall of Reach - Boot Camp and Halo: The Essential Visual Guide.


 * Throughout Halo: Contact Harvest, the Eridanus and Epsilon Eridani star systems are referenced as being one system: "Epsilon Eridanus". It is implied that both Reach and Eridanus II are situated in this system. With two exceptions, (a chapter heading in the first printing of Halo: The Fall of Reach and the "Reclaimer" entry in the Bestiarum), the two systems are regarded as separate in all other fiction; in Halo: First Strike, for instance, the main characters travel from Epsilon Eridani to Eridanus, a journey that would take days were it not for the Forerunner crystal from beneath CASTLE Base.


 * The Insurrection is described as being largely confined to the aforementioned "Epsilon Eridanus" system, whereas outer systems are described as being more stable due to their more homogeneous populaces. In other media, the Insurrection is depicted as occurring almost exclusively in the Outer Colonies and spanning numerous star systems. Additionally, the highly varied populations of the Outer Colonies are cited as one of the reasons for their instability. Prior to Contact Harvest, no mention was made of fighting breaking out in Epsilon Eridani; on the other hand, the conflict was described as being at its most active in the similarly named Eridanus system. This has been partly reconciled in later fiction, with the Insurrection being active in both systems, although the claim that the conflict at large was confined to Eridanus has been ignored.


 * Operation: TREBUCHET is stated to be the name for the UNSC's entire ongoing campaign against the Insurrectionists as of 2524. This contradicts Halo: The Fall of Reach, which establishes TREBUCHET as a single counterinsurgency operation against the rebels in the Eridanus system in 2513, one that is treated as an event long past by 2525. However, the in-game timeline in Halo Wars refers to Operation: TREBUCHET as "upcoming" in an entry dated 2520; furthermore, Halo: Mortal Dictata references TREBUCHET as the "last counterinsurgency operation against the colonies", lending more credence to the version presented in Contact Harvest.


 * In Halo: Contact Harvest, humanity is said to have seventeen planetary colonies. In a forum post, Joseph Staten suggested that a large number of the colonies are smaller settlements or outposts; he admitted to being "intentionally vague" in order to leave room for possible future expansion. Later media have ignored Staten's claim, showing that the Unified Earth Government had at least several dozen developed colony planets and had some presence on over 800 worlds.

Halo: The Cole Protocol
When Lieutenant Keyes is warned of the incoming Covenant fleet and asks what UNSC ships are nearby, the book first states that three destroyers are picketing, but immediately counters that the and three frigates would be unable to repel a Covenant assault. However, they are later confirmed to be destroyers, one of which is the.
 * Internal


 * External
 * According to Halo: The Flood, Jacob Keyes killed his first human with a pistol which is specifically stated to have a barrel; however, Halo: The Cole Protocol states he used a modified plasma rifle, a weapon which lacks any form of barrel.


 * Thel 'Vadam reacts to Jai-006's face-concealing Mjolnir helmet with extreme disgust, believing that only a "soulless and dead" being would hide his face. This is uncharacteristically hypocritical in light of the fact that many Sangheili combat harness variants have helmets that fully cover the wearer's face; it is unlikely Thel would so harshly condemn something that is a common practice among his own kind.


 * The Cole Protocol establishes the notion that the Sangheili stigmatize doctors and medical treatment, a cultural trait that is echoed in later works. However, in Halo: The Flood, Zuka 'Zamamee is treated by "medics" for wounds he received aboard Pillar of Autumn and this is never regarded as being something out of the ordinary, let alone disgraceful.

Halo Wars
In the level Dome of Light, after requesting the first Rhino to be deployed, the radio operator on the will identify the player as "Harvest Surface Command" even though the level takes place on Arcadia.
 * Internal
 * This may be because Spirit of Fire was still assigned to Harvest.


 * External
 * Although the Forerunner relic on Harvest is discussed by Captain Cutter and Professor Anders at the end of Halo Wars: Genesis, its discovery is treated as new information in the game's opening cinematic. The simplest explanation is that Forge's discovery of the relic in the cutscene takes place during the events of Genesis.
 * In all renders and cutscenes, most notably "She Is Not My Girlfriend" at the beginning of the level Anders' Signal, the M41 Light Anti-Aircraft Gun is shown with four barrels. It is likely that this is a variant of the M41 LAAG, similar in design to the M41 Extended Light Anti-Aircraft Gun mounted on the OF-92 Booster Frame.

Halo 3: ODST

 * External
 * The depiction of the city of New Mombasa in Halo 3: ODST differs significantly from its Halo 2 incarnation, the most prominent changes being the replacement of the Mombasa Tether to a separate island and a major restructuring of the island's general shape. As a result, the Prophet of Regret's assault carrier Solemn Penance is also moved to a different location over the city than it is in Halo 2.


 * In Halo 3: ODST, Solemn Penance is stationary just before jumping into slipspace, yet in Halo 2 during the closing cutscene of the level Metropolis, the assault carrier is moving forward.
 * During the same scene in Halo 3: ODST, the In Amber Clad is seen approaching the carrier in a straight line and is clearly separate when they jump, but in Halo 2, the In Amber Clad flies in an arc to a position underneath the starboard side of the assault carrier. These changes were made for the sake of drama and to make the scene easier to witness from the Rookie's point of view.

Halo: Helljumper
In the comic, Kojo Agu notes that Dutch makes a habit of never calling him by his nickname "Romeo" and instead by variants like "Romes". In Halo 3: ODST and Halo: New Blood, Dutch always refers to him as Romeo.
 * External

The Babysitter
According to Halo: The Fall of Reach, ONI's intelligence on the Prophets as of the briefing for Operation: RED FLAG on August 27, 2552 was extremely scarce; their appearance was unknown and their existence was only inferred from Covenant communications. Debriefings and helmet recorder data from the mission depicted in The Babysitter (which can be inferred to have occurred prior to November 2551 due to the MJOLNIR Mark IV armor still being in service) would no doubt have shed more light into the appearance and role of the Prophets, which would in all likelihood have been utilized in the Spartans' RED FLAG briefing due to the mission's critical nature.
 * External
 * This may be a retcon similar to later media ignoring the nature of the first human contacts with Sangheili, Jiralhanae and Mgalekgolo in The Fall of Reach and First Strike, though the statements about the Prophets remain unchanged in the revised edition of The Fall of Reach. This is probable since Linda-058 was deployed on a similar mission to assassinate a Prophet on Odenli'sh during the war.

Pariah
Jacob Keyes is shown to be aware of the reason behind Dr. Halsey's mission to observe the Spartan-II candidates. However, Halo: The Fall of Reach and Halsey's journal clearly indicate that Keyes was unaware of the mission's true nature, and that Halsey had him reassigned before he could find out.
 * External

Stomping on the Heels of a Fuss
Connor Brien is stated to have spent time on High Charity prior to the events on Beta Gabriel. However, evidence suggests that the UNSC had no knowledge of High Charity at this time. Brien was deployed to Beta Gabriel shortly following the Fall of Reach in August 2552. In the Halo 2 level Regret, which takes place on November 2, 2552, Cortana refers to the space station as "something called High Charity", indicating that she is entirely unfamiliar with it or its role as the Covenant capital. Cortana's previous mission was to be Operation: RED FLAG, an ONI Section III-initiated operation to locate and capture the Covenant's leadership. It is extremely unlikely that ONI would have chosen to withhold its knowledge of High Charity from her, given the supreme importance of RED FLAG.
 * External

The Mona Lisa
It is repeatedly stated that the UNSC has a policy not to take Covenant prisoners and the main characters are baffled when they discover Covenant prisoners aboard the prison vessel Mona Lisa. However, UNSC personnel are shown taking Covenant prisoners in Halo: The Flood, Halo Wars: Genesis, and several later sources. It is likely that the "policy" to which the characters refer is a guideline or standard operating procedure rather than an official protocol.
 * External

Palace Hotel
The specifics of the events of the ground battle in New Mombasa differ significantly between the Halo 2 level Metropolis and the Halo: Evolutions story Palace Hotel. In addition to extensive changes in dialog, several events and locations are described differently. For example, the scene in the parking lot of the Kilindini Park Cultural Center, featured in Palace Hotel, is not present in the game. The ending of Palace Hotel is also different from Metropolis, where John makes his way to a Marine outpost in a corporate building instead of a hotel. In the game, it is mentioned that the Marines' lieutenant was killed as soon as they arrived and that Sergeant Banks is in charge at the time, while in Palace Hotel, John meets the Marines' lieutenant at the outpost. Overall, Palace Hotel could be regarded as an alternate-continuity take on the story as presented in Halo 2, much as the Fall of Reach comic series is an alternate incarnation of the novel's story.
 * External

Human Weakness
Cortana knows about the death of Colonel James Ackerson while being held captive by the Gravemind on High Charity. However, the scene takes place days prior to Ackerson's death after the Battle of Cleveland sometime between November 8 and 17.
 * External

The Impossible Life and the Possible Death of Preston J. Cole

 * External
 * Vice Admiral Preston Cole is said to have had 117 ships under his command during the Battle of Alpha Aurigae. Halo Wars: Genesis states he had 107 ships in the same battle.


 * According to the story, two of Preston Cole's great-grandfathers served in the Rainforest Wars. However, the conflict took place more than three centuries before Cole's birth.
 * Cole's ancestors may instead have served in the ill-defined Inner Colony Wars.


 * There are multiple discrepancies involving Admiral Stanforth's name, age and rank; for a more detailed analysis, see here.


 * In Halo Wars: Genesis, the Halo Wars in-game timeline, and the pre-release timeline for Halo: Combat Evolved, Preston Cole is said to have been promoted to full admiral after his victory at Harvest. In The Impossible Life and the Possible Death of Preston J. Cole, no mention is made of his promotion and he is referred to as a vice admiral throughout the story, even as late as his final broadcast in the Battle of Psi Serpentis in 2543; Halo: The Essential Visual Guide also refers to him as a vice admiral. It is possible his rank expired or he may have been demoted in an unseen event.
 * The ONI memorial in Halo 3: ODST refers to Cole posthumously as a full admiral. However, the memorial is not a wholly reliable source given several other canonical inconsistencies with established media.


 * The CCS-class battlecruiser is said to have first been encountered at the Battle of Psi Serpentis in 2543. This contradicts Halo Wars: Genesis, which shows Cole's fleet engaging such vessels in 2526; Halo Wars, in which two CCS-class ships are encountered and identified as such at Arcadia in 2531; data pad 10, which states that the Assembly's findings about glassing were derived from observing the CCS class in 2526; and Halo: The Essential Visual Guide and the Halo Encyclopedia, which state that vessels of the class were encountered frequently throughout the war.


 * In reference to the Reach super-AI network, Cole states, "They're the only ones in the Outer Colonies with the raw power to get the job done." However, Reach is the most significant of the extrasolar Inner Colonies.

Soma the Painter
The Auditor and the Prelate agree to inform the Didact of the Flood's appearance at Seaward. However, Halo: Cryptum reveals that the Didact was in exile on Earth at the time and would not be revived from suspended animation until nearly three centuries after the events of the short story.
 * External

Halo: Blood Line
The smart AI Iona interfaces with Victor-101 through his neural interface, even using the system to force some of his memories to resurface, indicating that he has received the Spartan neural interface upgrade allowing such connectivity. The comic series is set prior to the finale of the Fall of Reach, indicating that Victor must have received the upgrade some time earlier. According to Halo: The Fall of Reach and a Bungie Weekly Update, John-117 was the first Spartan to receive the upgrade and neurally integrate with a smart AI on August 29, 2552; this is later corroborated by the data pads of Halo: Reach, in which the Assembly makes note of the melding of John's and Cortana's neural networks as a monumental achievement in their own goals.
 * External

Halo: Reach

 * Internal
 * During the level "Long Night of Solace", Colonel Holland once refers to the Covenant corvette Ardent Prayer as a cruiser.


 * In the game's introductory cinematic, the Covenant-conquered Reach is depicted as being only partially glassed; the data pads in the game explain the impossibility of the Covenant fully glassing a planet's surface, supported by statements of a similar nature in Dr. Halsey's personal journal; additionally, references to the complete glassing of Reach were modified in the 2010 reissue of Halo: First Strike. However, in the skybox of the multiplayer map "Condemned", Reach's surface is depicted as being almost completely ablaze, significantly different from the more subdued imagery in the game's introduction. This discrepancy may stem from the map having been created by a separate studio, Certain Affinity, who may not have been properly informed of the wider retcon regarding the Covenant's glassing capabilities or the specific instance of Reach's glassing.


 * External
 * In Halo: Combat Evolved and Halo: The Flood, which take place directly after Halo: Reach, the Marines on board the Pillar of Autumn are armed with MA5B assault rifles. However, in Reach, the Marines assigned to the Pillar of Autumn are armed with MA37 assault rifles.
 * From a game design perspective, this is due to Bungie declining to spend resources to create a weapon that would already have its place in the "sandbox" filled, especially given the relatively brief appearance it would make. From a canon perspective, it has since been explained that Marines will utilize Army weaponry should the situation require, as occurs in Halo: Reach.


 * According to an Intersystem News sheet that comes with the Limited and Legendary editions of the game, Jacob Keyes was already a captain in 2550. However, according to Halo: The Fall of Reach, he was not promoted to captain until after he performed the famous Keyes Loop in July 2552.
 * This could be an in-universe research error.


 * Halo: Reach places Olympic Tower in the city of New Alexandria. Halo: The Fall of Reach states that the building was part of Reach's Fleet Command Headquarters, which is implied by The Fall of Reach and First Strike to be located within the Reach FLEETCOM Military Complex in the Highland Mountains as opposed to a civilian city. Halo: Reach also gives no indication that Olympic Tower is part of a larger FLEETCOM complex. Additionally, the game depicts New Alexandria's conquest and glassing on August 23; the FLEETCOM HQ was still intact as of August 30 in The Fall of Reach, as the book has the Covenant launch an overwhelming ground assault to take the HQ.


 * The placement of the multiplayer map "Breakneck" in New Mombasa is inconsistent with the city's Halo 3: ODST incarnation. Assuming the locations of the city's landmarks, such as the bridge of the Uplift Nature Reserve, are consistent with ODST, the map should be situated near the southernmost main section of the Reserve. No skyscrapers or streets are present in the area in ODST. In addition, according to the player's HUD compass, the city center and the Mombasa tether are situated to the south and southwest of the map, respectively. Based on the way the city is presented in ODST, the aforementioned landmarks would be located to the north and northwest of the Uplift Reserve and thus the map's playable area.


 * While stated to be set on Installation 04, the skybox of the map "Ridgeline" features a prominent Earth-like world with visible continents and oceans as opposed to the gas giant Threshold.

Halo: Fall of Reach

 * Internal
 * When the Spartans are issued their original Mjolnir armor the plating is free of any markings. All subsequent panels show the Spartans' tags on their chestplates.
 * When Halsey puts on John's helmet for him, the helmet in her hands resembles the Mark VI's, with its raised brow, oval visor groove, and square mouth guard. In the next panel it is now the Mark IV helmet, with its lowered brow, sleeker shape, and large breathing ports.
 * The bonus layout artwork for Covenant shows the Spartans wearing the Mark VI-style armor from "The Package" in the initial sketches, though it is changed to Halo Wars-style Mark IV armor before the inking and coloring. It may be that the Mark VI in Halsey's hands is likewise an error that was missed in the correcting phase.
 * During the skirmish between the Unrelenting and the, Captain Wallace orders for a Shiva nuke to be fired at the Covenant ship and for their MAC to be fired. Just as the nuke is launched, a bridge officer confirms the Commonwealth MAC has charged to 100%. The nuke impacts the Unrelenting, dropping its shield and causing some damage near the bow, but the MAC is never seen being fired or impacting.
 * When Blue Team struggles with opening the door leading inside the Unrelenting, they appear to still be in vacuum. However, a Jackal without any breathing gear fights them after the door opens.
 * In the book, the first door to the interior of Unrelenting opened automatically, then shut to restore the atmosphere, with the second one having to be manually opened. The comic appears to have skipped the previous door and a comment from Kelly about the size of the door implies that it is the first one they encountered.
 * When the Spartans are briefed about Operation: RED FLAG, Halsey reports ONI has just discovered a new Covenant species, the Prophets, and shows an image of the Prophet of Truth. Yet in an earlier issue, taking place in 2525, the Spartans, Halsey, and Vice Admiral Stanforth watch a broadcast from the Prophet of Regret himself, who displays his image quite visibly.

Halo: Fall of Reach departs from the source novel in numerous instances, with many liberties taken to better suit the comic medium. As it is not a particularly strict adaptation of the novel, one may regard it as an alternate interpretation of the original story, as opposed to an unintentionally contradictory narrative or a retcon. For a list of differences between the novel and the comic adaptation, see here.
 * External

Halo: Cryptum

 * Internal
 * Bornstellar concludes that the device used to camouflage the central island of Djamonkin Crater must be a baffler instead of a dazzler after witnessing its effects. However, he later refers to it as a dazzler.


 * The Librarian is said to be older than the Didact at "over eleven thousand years" of age, yet previously the Didact is mentioned to have served as protector of the ecumene for twelve thousand years.

Six Halos are described holding station over one of the Arks, which Halo: Silentium establishes as the greater Ark. However, Silentium clarifies that the newer array of six Halos was manufactured by (and hidden at) the lesser Ark. There is no apparent reason for the six rings (the Forerunners' carefully guarded last resort) being temporarily transported to the greater Ark.
 * External

Halo: Glasslands

 * External
 * At the conclusion of Halo: Ghosts of Onyx, Onyx dissolves into trillions of Sentinels that vaporize any vessels nearby and remain to guard the slipspace rift to the shield world formerly in the core of the planet. These Sentinels are wholly absent in Glasslands, in which UNSC vessels are capable of traversing the former site of Onyx, now said to contain a debris field, without any sign of threat. While the Onyx Sentinels are mentioned in passing when referencing the events of Ghosts of Onyx, their disappearance is neither noted nor explained.


 * Lieutenant Commander Kurt Ambrose is referred to as "Lieutenant" Ambrose.


 * Admiral Parangosky states that Dr. Halsey escaped with "billions of dollars' worth of UNSC resources". The reference to dollars is out of place, as the credit is the standard currency within the UEG; previously, for example, a reference to "dollars" in a contemporary setting was retconned to "credits" in the 2010 reissue of Halo: The Fall of Reach.


 * During one of her briefings to Kilo-Five, Captain Serin Osman operates under the presumption that the existence of Onyx, as well as Parangosky's cover-up of the planet, should be common knowledge. None of the members of Kilo-Five shows any indication that they were unaware of the planet beforehand. Onyx was removed from all navigation charts and databases in 2511, before most members of Kilo-Five were born. As such, the rest of Kilo-Five, apart from Osman and Black-Box, would have no way of knowing that a planet called Onyx existed in the first place, much less that Parangosky had classified it. While it is possible that some information about the planet did leak out to the public (as suggested in Halo Wars: Genesis), Osman's assumption that non-ONI personnel would be familiar with a single, obscure planet among humanity's hundreds of colonies is highly doubtful.


 * Captain Osman claims that the UNSC had captured and defused a Huragok "a couple of years ago", and that ONI has made several technological developments by reverse-engineering the data it contained. She implies the Engineer had died and states that ONI needs more than one Huragok so they can repair each other and reproduce. Strangely, she does not mention that several Huragok were rounded up aboard the when it returned to Earth, nor does she say that one was rescued from New Mombasa and interrogated shortly thereafter. It is possible that she refrained from telling the whole truth to motivate her team to board Piety and capture the Engineer aboard.


 * There are a number of conflicts involving Dr. Halsey's theft of the rebel vessel Beatrice. Halsey is repeatedly stated to have "hijacked" the ship (even in one of her internal monologues) and it is implied that she threatened someone with her personal sidearm when she stole the vessel, an incident which CPO Mendez uses grounds for confiscating her pistol. Halo: First Strike describes the event in question, and no threats are involved when Halsey boards the vessel (which is empty and unguarded) and leaves unopposed. Additionally, Mendez refers to the incident as if he had been present, even though he did not have first-hand knowledge that Halsey had stolen a ship; him knowing about the event would be based on Blue Team's or Halsey's accounts. Mendez was also not aware of Halsey's ulterior motives for bringing the Spartans to Onyx, as she had divulged that information only to Kurt Ambrose in private shortly before the group entered the shield world, casting Mendez's paranoia about her in a questionable light. Furthermore, Mendez treats the incident as if Halsey had stolen a friendly vessel; Beatrice was in fact the personal ship of Governor Jacob Jiles, an Insurrectionist leader whom hours prior had threatened to destroy a UNSC frigate. Most egregiously, Admiral Parangosky lists the theft of Beatrice as one of the war crime charges brought against Dr. Halsey following the latter's arrest on Trevelyan.


 * According to Halo: Glasslands, Dr. Halsey did not have an AI to help her decipher Forerunner symbols while in the shield world. However, she had the "micro" AI Jerrod in her laptop in Halo: Ghosts of Onyx, helping her translate Forerunner symbols while they traversed the interior of Onyx. No mention was made of Halsey losing Jerrod, and she still has her laptop after she and the other survivors had entered the shield world.


 * During an argument with Dr. Halsey, CPO Mendez claims the SPARTAN-III program lacked any form of genetic filtering. In Halo: Ghosts of Onyx, Mendez is present at a meeting where it is established that the SPARTAN-III program did indeed have a set of genetic qualifications, a necessity because the biochemical augmentations at the time were compatible only with a particular series of genetic markers and that any deviations would carry a significantly increased risk of failure. For this reason, the initial pool of candidates for Beta Company had to be reduced from the original projection of nearly 1,000 to 375. His argument is based on the alleged lack of genetic screening making the SPARTAN-III project more morally sound than the SPARTAN-II program due to the latter's perceived elitist overtones because of its strict genetic criteria. However, this disregards that the screening was in place not only for the sake of the SPARTAN-II augmentations but also to ensure that the candidates would be fit both physically and psychologically to acclimatize to the harsh military life imposed upon them, facts of which Mendez was fully aware.


 * Lucy-B091 lashes out in a fit of rage and strikes Dr. Halsey in the face with strength enough to "send a shock wave right up her arm" and leave her hand "throbbing"; based on the description of the incident, Lucy clearly exhibits no self-control in the assault. Halsey quickly recovers and does not suffer more apparent injury than a slightly bleeding nose. Based on prior evidence of the Spartan-IIIs' physical strength, combined with the SPI armor's hardened gauntlet plating (as seen here and here, the knuckles and fingers are reinforced with metallic armor), such a blow would have inevitably resulted in Halsey's death. Spartan-IIIs have been stated to possess the strength of "three normal soldiers", and while Lucy is twenty at the time, Spartan-IIIs have been described as being capable of matching Sangheili and other Covenant in close quarters at only twelve years of age, effortlessly snapping the aliens' necks and limbs, demonstrating strength that would certainly be lethal against a frail, aging human. Although Glasslands offers Lucy's small size as a justification for the meager force of her punch, Halo: Ghosts of Onyx gives no indication that her physical prowess is in any way anomalous among the Spartan-IIIs as she is able to keep up with the decidedly superhuman feats of the rest of her fireteam and the rest of Beta Company during Operation: TORPEDO and subsequent operations. Not only this but even a small Spartan-III, in armor no less, who delivered a blow with enough force to feel a shockwave to their shoulder would inflict devastating damage on their target.


 * In Halo: Ghosts of Onyx, the omniscient narrator states that Lucy-B091 would remain mute for the rest of her life following Operation: TORPEDO. However, Lucy overcomes her post-traumatic vocal disarticulation and regains the ability to speak in Glasslands.


 * Lucy-B091 consistently internally refers to Kurt Ambrose only as "Kurt" despite the fact the Spartan-IIIs knew him by his rank and surname; in Halo: Ghosts of Onyx, only the Spartan-IIs and Dr. Halsey refer to him as "Kurt".


 * Glasslands implies Naomi-010 and, presumably, the Spartan-IIs as a whole, did not know about the flash clones used to replace them. In Halo: The Flood, a section from John-117's point of view indicates he is aware of the clone replacements, and both Halo: Fall of Reach and Halo: The Fall of Reach - The Animated Series depict several Spartan-II candidates seeing their flash clones as they are abducted.


 * Dr. Halsey notes in an internal monologue that she had decided it was "kinder" to tell the Spartan-IIs who survived their augmentations that Serin-019 had been killed in the procedures rather than revealing that she had been cripplingly injured; earlier in the book, Naomi-010 tells Serin that she believed the latter had died during the augmentation procedures. In Halo: The Fall of Reach, the live washouts accompany the successfully augmented Spartans to the closed-casket funeral for those who died. John-117 is later shown to be aware of the fate of the washouts, internally noting that the dozen crippled Spartans had been reassigned to ONI. While it can be inferred that Serin was excluded from the funeral ceremony, it is suspect that Halsey would lie about her fate for the sake of kindness given that she allowed the successfully augmented Spartans to see the other washouts, many of whom were crippled far more severely than Serin.


 * When the survivors in the shield world reestablish contact with the UNSC, Admiral Parangosky tells Dr. Halsey that it has been "five months" since John-117 and Cortana went missing after stopping the Halo Array from firing. However, John and Cortana disappeared on December 11, 2552, with the UNSC receiving confirmation of this when the Arbiter returned to Earth on December 23. The scene with Parangosky informing Halsey about their disappearance occurs in February 2553, so fewer than three months had passed at that point. Even considering the possibility that Parangosky may have lied, she would have no reason to do so, as both she and Halsey were aware of a transmission sent by Cortana on November 3 - fewer than four months earlier - in which she announced that John was on his way to Earth.


 * When describing the Spartan-IIIs, Vasily Beloi notes that "If they'd been pumped full of growth hormones and ceramics like Naomi, then it hadn't worked. They were just regular-sized kids." This is inconsistent because the Spartan-IIIs' bodies are described as decidedly atypical for their age in Halo: Ghosts of Onyx. Lucy-B091 is mentioned as being abnormally small for a Spartan-III with a height of 1.6 meters at the age of twelve. Additionally, at twelve years old, the Spartans of Gamma Company had grown to near-adult size because of hormonal supplements, and are compared to Olympic athletes years older due to their "well-muscled" and "sculpted" physiques, making it unlikely for anyone to assess them as "regular-sized kids". Halo: Last Light reiterates that most of the Spartan-IIIs are conspicuously larger than normal humans (with Lucy as a noted exception), and similar to the statements in Ghosts of Onyx, it is observed on several occasions that the Gamma Company Spartans' physiques are clearly not consistent with their age.


 * Glasslands maintains that Dr. Halsey attempted to hide the SPARTAN-II flash clone replacement operation from the upper echelons of ONI; Admiral Parangosky claims that she did not learn about the clones until years afterward. When referenced in previous fiction the flash cloning operation is never singled out as something separate or particularly secretive in comparison to all other aspects of the program; on the contrary, ONI is unanimously identified as the chiefly responsible party as opposed to Halsey alone. In Halo: The Fall of Reach, John-117's classified file, accessed by Cortana, refers to the replacement operation as an "ONI black op". In Halo: First Strike, Halsey refers to the "old flash clone techniques that ONI had used to replace the originals". In her journal, Halsey refers to the clones like any other part of the program, failing to mention any attempt to conceal it. Furthermore, Halo: First Strike notes that Colonel James Ackerson had the clones monitored as they grew up and even had the bodies retrieved after they died, which calls into question Parangosky's statements of not learning about the cloning operation until years later. It is also suspect that Halsey would see it necessary to conceal this particular aspect of the program from ONI, given their oft-demonstrated neglect for moral concerns, particularly where the secrecy of their operations is concerned. Had there been an attempt to withhold information, it would have been futile from the beginning; the dozens of ONI scientists and field agents that carried out the operation would have relayed the information to ONI's leadership in the unlikely event that the ONI surveillance of the program failed to do so.
 * Parangosky may have lied about Halsey's cover-up of the flash-cloning operation, setting her up as ONI's scapegoat for the morally abhorrent actions of the SPARTAN-II program. Parangosky thus could have charged Halsey with the false cover-up in addition to the genuine war crimes for which she was arrested to settle the personal vendetta between them. However, the doctor makes no attempt to dismiss the admiral's claims as false. Indeed, both characters' internal monologues indicate that the cover-up actually occurred. Halsey's failure to defend herself is noticeably contrasted with the subsequently-released 16th issue of Halo: Escalation, in which she responds to Commander Sarah Palmer's similar accusations thus: "You can't be that naive. You really think I could have pulled off everything I've been accused of without the full support of ONI? Of the entire UNSC? Consider the resources. The budgets. You think those decisions were made unilaterally? Whether it was a signed form or a wink — they approved it all."


 * The Sangheili repeatedly refer to Fleet Admiral Hood as "Shipmaster of Shipmasters". While not strictly a contradiction, it is somewhat out of character for the Sangheili to insist on using such an epithet. Hood's rank would draw more natural comparisons to the actual Sangheili ranks of Supreme Commander or Imperial Admiral rather than a neologism contrived from the lesser rank of Shipmaster.

Halo: The Thursday War

 * External
 * The carries a large arsenal of nuclear weapons aboard and is yet capable of remaining completely undetected over Sanghelios. According to Halo: Ghosts of Onyx, this would be impossible, as the plutonium in nuclear weapons negates any stealth measures upon slipspace transition by emitting an easily detectable Čerenkov radiation signature, forcing even stealth vessels to jettison any onboard nukes in order to perform a cloaked slipspace exit.
 * Port Stanley had been heavily upgraded with Forerunner technology, so it is possible that this flaw had been alleviated (although no such upgrade is mentioned).


 * Dr. Catherine Halsey is portrayed as being entirely unfamiliar with the concept of a fourth-generation AI and appears to believe Black-Box when he falsely claims that fourth-generation AIs are created by other AIs (after the exchange, Black-Box tells Evan Phillips that he was lying about his generation being created by other AIs). However, in Halo: Ghosts of Onyx, Halsey demonstrates close familiarity with fifth-generation smart AIs and has an intimate understanding of their behavior; she is able use a Zen koan to attract the attention of the fifth-generation AI Endless Summer, states that fifth-generation smart AIs like to "show off", and mentions that she wrote the subroutines that allow Endless Summer to lie.
 * It is possible that Halsey feigned ignorance out of unwillingness to help Admiral Parangosky's underlings, who were responsible for her arrest and regarded her with open contempt. However, Black-Box would most likely have known the full extent of her expertise given his unrestricted access to her and ONI's files, unless Halsey managed to hide this information from ONI at large. Regardless, he appears to regard Halsey's ignorance about the development of fourth-generation AIs such as himself as genuine.


 * While on Trevelyan, Jul 'Mdama is said to be able to determine the passage of time based on the "position of the sun". Given the structure's nature as a full-size Dyson shell, this would be impossible, as the sun would always be directly overhead at any point on the sphere's interior surface.


 * A Sangheili insult for humans - nishum - is said to roughly mean "intestinal parasite". The name is derived from the Sangheili mistaking armored humans for creatures with exoskeletons, then after examining dead human bodies concluding that they are parasites inside insectoid beasts. However, the Sangheili themselves wear body armor (which is often thicker and more carapace-like in design than standard human infantry armor), as do most of the Covenant species, so it seems suspect of them to not be able tell that humans wear artificial armor just like they do.
 * During a scripted conversation on the Halo 5: Guardians level "Before the Storm", a member of the Swords of Sanghelios refers to fellow Sangheili Sali 'Nyon as a nishum. This may indicate that the term has been retconned into a general insult, discarding the suspect explanation provided in The Thursday War.


 * Dr. Halsey asks Black-Box "So which ship or Spartan are you assigned to?" upon encountering the AI. This question excludes a broad range of assignments in which AIs are commonly known to serve, while equating Spartans with ships as one of two noteworthy posts for AIs; Halsey would have no reason to presume that an AI would be assigned to a Spartan, given that Cortana's assignment to John-117 was a one-time exception and not a standard procedure among Spartans.


 * Fleet Admiral Hood is suggested to be antagonistic toward Dr. Halsey; he assures Admiral Parangosky that Captain Del Rio is "Halsey-proof" and that the doctor will not be able to "manipulate" him. In previous fiction Hood is portrayed as one of Halsey's closest friends and allies within HIGHCOM, harshly censuring Colonel Ackerson for mocking the doctor and her Spartans and lamenting Halsey's apparent death on Reach.
 * It is possible that Hood became resentful of Halsey after she drew Blue Team (and consequently an entire Navy battle group) away from the defense of Earth on the premise of needing Spartans to secure Forerunner technology, when in reality she planned to hide out on Onyx.


 * Professor Evan Phillips casually mentions that it is common for Forerunner portals to displace individuals to different planets as if this information is common knowledge, even though there is no precedent for such technology in previous fiction nor any evident reason for Phillips being informed of how Forerunner portals operate (he is a xenoanthropologist specializing in Sangheili culture).

Halo 4: Forward Unto Dawn

 * Internal
 * John-117 claimed that the Battle of Circinius IV resulted in the entire population, with the exception of Hestati squad, being annihilated. However he goes on to save more survivors years later in Operation: PHALANX, creating a major contradiction.


 * External
 * In Halo 4, it is implied that coordinate data from an incident with the Composer from Installation 03 led to Requiem. No mention is made of Infinity picking up Cortana's distress call which results in the ship and its battle group making a slipspace jump toward Requiem in Halo 4: Forward Unto Dawn. Although Infinity receives the distress call in Halo 4, this appears to be after the ship is already near Requiem; in Forward Unto Dawn, the signal is picked up while Infinity is still light-years away, as evidenced by the crew having to enter cryo-sleep for the journey.
 * Forward Unto Dawn also depicts a considerably different interpretation of Cortana's introduction as depicted in the game. In the game her avatar simply winks into existence when intruders are detected aboard the ship; she then calmly (though hesitantly) revives John with the words, "Wake up, Chief. I need you." In the web series, however, Cortana experiences a series of violent personality shifts (at one point vowing to let John die with her) until the Dawn ' s sensors detect Requiem. Cortana's avatar then dramatically fades from a large sphere to a much smaller point, from which she then appears. She then wordlessly begins thawing the Master Chief's cryo chamber without using the holographic terminal seen in the game. In the level Dawn Cortana claims to be unaware of the ship's proximity to Requiem; however, she should have been able to see it through her neural link with John, so she was likely either joking or undergoing the effects of rampancy.
 * Halo 4: Forward Unto Dawn depicts a fleet of more than two dozen cruisers and frigates accompanying Infinity to Requiem. The Commissioning shows only two s by the time Infinity has reached Requiem, though the camera angle obscures any other ships that may be present. Regardless, this escort fleet is never mentioned in the game.
 * The fleet may have been sent to deal with the Covenant ships still in orbit above Requiem. However, the fleet is never mentioned during the level "Shutdown", when it could have been used to intercept Mantle's Approach before the Didact could escape Requiem.
 * At the end of the web series, most ships in the fleet are shown entering slipspace under their own power. However, some of the vessels hold formation so closely to Infinity that they may have entered its slipspace rupture and followed its wake; the two closest frigates maintain the same formation as those seen in The Commissioning. It is possible that these ships arrived alongside Infinity while the rest of the ships were outpaced due to their slower engines, thus explaining the frigates seen in the trailer. They may have been destroyed when Requiem began pulling the flagship inside, explaining the high volume of debris seen cascading toward the shield world.

Scanned
Linda-058 and two other female Spartans are portrayed with long hair during the Spartans' augmentation procedures. According to Halo: The Fall of Reach, all of the Spartans had their heads shaved in preparation for the procedure.
 * External

Halo 4

 * Internal
 * John-117's size varies from cutscene to cutscene. John is five inches taller than Sarah Palmer; they are 7' 2" and 6' 9", respectively. However, in the level Infinity he is only minutely taller than her while in the Epilogue he towers over her by about two feet.
 * The Spartan Ops cutscenes depict weapon strengths at levels exaggerated from gameplay. For instance, Thorne in Scattered is able to kill two Sangheili Storm with a storm rifle with a single shot each, and Sarah Palmer in Invasion kills Promethean Knights with a single shot from a magnum. Energy shields are also never depicted on Spartans, Elites, or Knights, with weapons damaging them as though they had no shields.
 * 343 Industries writer Jeff Easterling has implied that the instance with the Prometheans is non-canonical.


 * External
 * During the prologue set in the Human-Covenant war era, Spartan-IIs are depicted wearing post-war era MJOLNIR armor rather than war-era MJOLNIR armor. The Halo 4: Essential Visual Guide allegedly claims that it's an older variant that acts as a precursor to Mark VI Gen 2, however former Creative Director, Josh Holmes, concurrently stated "We didn't have time to build S-II armor just for intro so we used the S-IV armor in its place. Canonically incorrect I know. :(" and "the story is canon, the specific armor representing that story is not. Does that make sense?", creating a major contradiction.
 * The had a  design where Halo 3 left of, while Halo 4 picks ups with it suddenly changing to a  design.
 * This has since been clarified as merely an artistic interpretation due to behind-the-scenes developmental reasons; the Halo 3 design for the Dawn is still considered the canonical design by 343 Industries.
 * In John-117's accessible service record in the level "Dawn", Pillar of Autumn (a Halcyon-class cruiser) is misidentified as a frigate.
 * The Cryptum that preserved the Didact on Erde-Tyrene in Halo: Cryptum left him very weak, and he had to be reinvigorated through a nutrient bath to regain his strength, a process that took several days. In Halo 4, the Didact's Cryptum has preserved him perfectly for over a hundred millennia and he has not suffered any kind of muscle loss.
 * According to Halo: Silentium, the Cryptum the Librarian imprisoned the Didact in is a "combat Cryptum", though the nature of this variant is never elaborated upon.
 * The Didact, in both his forms, is depicted with thick, spike-like protrusions in the place of hair; he is described as having a patch of pale, bluish white fur as in The Forerunner Saga.
 * Slipspace is described as an entirely featureless, pitch-black void in written media, a direct result of its inherently "nonvisible" nature.   In the level Midnight, though, slipspace resembles a bluish expanse with white streaks of stars being flown past. Likewise in the opening cutscene of Departure slipspace appears as a kaleidoscope of colors. This may be from both ships using Forerunner slipspace engines, which have been observed to create differing environments.
 * In his journal entry in the Infinity Briefing Packet, Gabriel Thorne expresses uncertainty as to whether the Master Chief was the only Spartan-II. This is strange since the Spartan-IIs and their exploits were highly publicized by ONI Section Two and were widely known among both the military and the general populace throughout the final years of the Covenant War, with rumors of them having circulated for years prior.
 * The terminals introduce many incongruities with The Forerunner Saga. However, 343 Industries have clarified that the terminals are a condensed version of the more complex story in the novels and should not be taken as a literal account; in-universe, this is explained with the unreliability of the Domain, through which the terminal records are presented.

Halo: Silentium

 * Internal
 * It is established that Path Kethona is the Forerunners' name for the Large Magellanic Cloud, which is correctly stated to be 160,000 light-years from the Milky Way. Later, when Audacity completes its second jump toward Path Kethona, the middle distance from the Orion complex is stated to be 87 million light-years, or 60 million light-years from the galactic border.
 * The reference to millions of light-years instead of thousands is likely a typographical error.


 * External


 * In Halo: Cryptum, the Didact states that he told the Librarian what the Primordial had said to him at Charum Hakkor and that her research had changed drastically as a result. In Halo: Silentium, the Librarian claims that while the Didact told her about the Primordial, he did not reveal what it had said to him, and the Librarian would not find out herself until thousands of years later when she journeyed to Path Kethona.


 * The timescales of the histories of the Forerunners and their contemporaries appear to have been extended considerably from those discussed in Halo: Cryptum. In Silentium, events hundreds of thousands of years past are discussed routinely, whereas in Cryptum, it is mentioned that the Forerunners had little records from only fifty thousand years earlier. For example, in Cryptum it is stated that early humanity began expanding their civilization outward to the galactic margins around 150,000BC. Boundless is noted to have been studying humanity's expansion to the same regions a million years earlier.

Halo: Initiation
The first issue of Halo: Initiation references Sarah Palmer as a lance corporal, and later corporal, during her ODST career immediately prior to her recruitment into the SPARTAN-IV program; this is corroborated by by Catalog. According to Palmer's biography on the now-defunct official Halo 4 website, she spent much of her Marine career as a lieutenant. Captain Del Rio calls Palmer a lieutenant when ordering her to apprehend John-117 in the Halo 4 level Reclaimer, although the context of this line has since been changed with the reworking of the rank structure of Spartan Operations; Del Rio now canonically addresses an off-screen Navy lieutenant. Halo 4: The Essential Visual Guide states that Palmer's leadership skill was the primary reason for her selection as a Spartan; if Palmer were a lance corporal, it is unlikely that such qualities could even be ascertained, as a lance corporal would have virtually no command experience. While it is possible that she was demoted prior to the events of Initiation, this is not indicated in the comic; Jun-A266 congratulates her for her promotion to corporal, and no previous demotion is mentioned at any point. Thus, it is likely that her background as a lieutenant has simply been ignored.
 * External

Halo: Mortal Dictata

 * Internal
 * According to Halo: Mortal Dictata, Dr. Graham Alban's suicide occurred in 2523. However, the reference to the Covenant in his suicide note dates his suicide to 2525 or later. This was later rectified in the 2019 edition of the novel correcting the year to 2532.


 * External
 * According to a video clip of the early days of Spartan-II indoctrination shown to Naomi-010 by Black-Box, Dr. Halsey lied to Naomi that her father had approved of her conscription and was not expecting her to return home. In Halo: The Fall of Reach, Halsey specifically states, contrary to Déjà's recommendations, that they will not attempt to lie to the children about their parents to motivate them out of risk that the Spartans may go rogue if they ever learned the truth. Halsey's notes in her her journal correlate with the version given in The Fall of Reach, noting that "They deserve as much truth as we can stomach to tell them." ONI recordings described in Mortal Dictata also show the SPARTAN-II children exhibiting more extreme reactions to their abduction than Dr. Halsey's observations in her journal let on. However, descriptions in Halo: The Fall of Reach are more in line with the journal's suggestion of the children being mostly calm and compliant, as it is established that their ability to cope with the intense psychological strain involved with the program was one of the criteria for their selection. The comic adaptation Halo: Fall of Reach - Boot Camp corroborates this in an added scene in which Halsey and Déjà observe that none of the children are crying during their first days in the program. Mortal Dictata also claims that the Spartan children were based deep underground in CASTLE Base in the first three days of the program, even though Halo: The Fall of Reach describes them being relocated to a barracks on the planet surface in the Reach FLEETCOM Military Complex immediately after their induction (though they did train at CASTLE later on in their training). As stated in The Fall of Reach, the first days' extreme physical training and education sessions were arranged specifically to prevent the children from having time to think about their predicament, yet the nature of the sessions described in Mortal Dictata allows the latter scenario to occur. The three days in CASTLE base could also not have occurred prior to Halsey's introduction to the program, as the children had only recently been awakened from cryo-sleep at the time and were only informed of their new purpose during Halsey's induction session. The military-oriented focus, intense pace and ruthlessness of the initial training are also nowhere to be seen in Mortal Dictata ' s descriptions, which suggest a comparatively leisurely acclimation period.
 * In light of these contradictions, it is not out of the question that ONI tampered with the records or simply forged footage to make Halsey's part in the program look more morally reprehensible as part of their campaign to smear her reputation; or, more specifically, to manipulate Naomi in particular. Indeed, while the aforementioned footage is said to be from official recordings Naomi is watching on a data pad, it is ambiguous how much of the sequence described in the book is factual as Black-Box is directly interfacing with Naomi's mind through her neural implant to trigger her childhood memories and repeatedly points out the fallibility of human memory prior to the session.


 * The SPARTAN-II candidate abduction process is depicted with several incongruities. Retrieval team Theta 2 is shown to first kidnap Naomi and transfer her clothes to the flash clone, which is only then released (several kilometers from the spot where she was originally taken) but not before Naomi temporarily escapes, causing the operation to last several hours. This drives her family to panic about her disappearance and an extensive search operation is organized before her clone is found. The need to transfer the real Naomi's clothing to the clone is questionable, given that Halo: Fall of Reach, Halo: The Fall of Reach - The Animated Series and Scanned depict the clones wearing duplicate clothing, enabling ONI to switch the children on site and thus removing the need for a potentially suspicious disappearance before the clone is returned.


 * Staffan Sentzke matter-of-factly references the Flood's arrival on Earth during the Battle of Voi, yet Staff Sergeant Geffen gives no indication that a civilian should not be aware of this occurrence. Halo: Spartan Assault states that glassing of the Tsavo region (in reality meant to cauterize the infestation) was officially declared a Covenant sneak attack to prevent knowledge of the Flood from leaking to the public.


 * Black-Box references Dr. Halsey's termination of Araqiel as a cold-blooded murder; he makes a similar suggestion in The Thursday War. In spite of his personal dislike of Halsey, Black-Box (a high-level ONI AI) should be able to acknowledge that purging AI constructs was a relatively common practice throughout the war as part of the Cole Protocol, yet he regards the incident as a unique act of cruelty without precedent. It is strange that BB is aware of the incident in the first place, as CASTLE Base had been evacuated of personnel at the time and any means of off-planet communication had been cut by the Covenant long before. BB also blatantly disregards the context of the incident as detailed in Halo: First Strike: not only was Halsey acting in self-defense, with Araqiel threatening to kill her, but her actions were also in accordance with ONI's Operation: WHITE GLOVE, which entailed the destruction of any remaining AI in the facility to prevent their capture by the Covenant (although Halsey had not yet formally implemented the protocol at the time). WHITE GLOVE also forced Halsey to destroy Kalmiya, one of her personal AIs, something Black-Box never mentions when referencing the incident.


 * Plasma torpedoes aboard Pious Inquisitor are referenced as physical munitions stored in a dedicated "torpedo bay". In previous fiction, plasma torpedoes have been established as shaped agglomerations of electromagnetically-guided plasma, not unlike the bolts fired by handheld plasma weapons. The "torpedoes" are brought into existence at the time the weapon fires and do not exist in any meaningful capacity aboard the vessel.
 * The references to "plasma torpedoes" can be interpreted as referring to the ship's supply of superheated plasma used to generate the torpedoes, although the wording used suggests that the torpedoes themselves are stored aboard the ship.

Halo: Escalation

 * Internal
 * In Issue #15, the Zealot conversing with Jul' Mdama at the start changes armor styles and colors between panels. Initially he wears white armor in the likeness of Halo: Reach ' s Zealots, then on the following page he has red armor in the likeness of Halo 4 ' s Zealots.
 * The Janus Key's red and blue halves frequently swap colors in between issues.
 * In Issue #20, Dr. Glassman faints from the smoke and Palmer has Tanaka carry him. Subsequent art depicts him standing and running in multiple panels before Tanaka informs the others that he is "waking up".


 * External
 * As in Spartan Ops, energy shields are never depicted on Spartans or Elites, leading to instances like Thorne being severely wounded from a single Needler shot in Issue #22.
 * Issue #9 reveals the Ur-Didact's plan to use a Halo against Earth, killing all life on the planet shortly after his attack on New Phoenix. However, the Didact's opposition to using the Halos is presented as one of his core values in earlier fiction, serving as the impetus for his first exile in Halo: Cryptum. Halo: Silentium shows that he continued to abhor the thought of activating the Array even after his mental torment by the Gravemind drove him to enact his crusade against humanity.
 * The Didact's willingness to use a Halo likely stems from his second, 100,000-year exile on Requiem, during which he was isolated from the Domain and most other external stimuli. This solitude led him to dwell on his hatred of humanity for millennia, culminating in his willingness to forsake one of his most sacred principles and commit genocide. The Didact may regard his actions in a similar manner to the Conservation Measure: though the majority of humans would perish, the millions composed in New Phoenix would live on in digital form.
 * In Issue #10, the Ur-Didact is defeated by launching Installation 03's control room, with him in it, into the Composer's Forge, resulting in the Composers stored there activating and composing him. In Halo 4 Terminal 6, the Didact claims that his most recent mutation renders him immune to the Composer, hence why he was the only Promethean who did not become mechanical like the rest. This is supported by the final level of Halo 4, Midnight, where the Didact is seen floating inside his Composer's actively firing beam without any ill effects.
 * As the Composer's Forge held multiple Composers, it may have been that several composition beams rather than just one were enough to override his immunity. However, this raises the question of why he could not have used multiple Composers on himself at the time of the Forerunner-Flood war, given his seemingly free access to the Composer's Forge.
 * The discrepancy is joked about in Halo 5: Guardians, where the Unggoy Dimkee Hotay may remark: “I knew the Didact. He said like three words. Three! He said ‘I can’t be Composed’.”
 * In Issue #22, Catherine Halsey answers a hypothetical scenario in which she is asked whether she would enslave a sentient species for a chance at a Flood vaccine or cooperate with them for a slightly smaller chance, by saying she would take the former route of sacrificing many for the few. In Halo: First Strike, Halsey tells John she has tired of sacrificing many for the few, feeling guilt over her past actions and saying she should have tried to save everyone rather than settling for the majority. This informs her abduction of Kelly-087 later in the novel, as well as her attempt to sequester Blue Team and the Spartan-IIIs inside Shield World 006 in Halo: Ghosts of Onyx.

Halo: Broken Circle

 * Internal
 * In Chapter 14, the narrator mistakenly refers to Trok 'Tanghil as Ernicka the Scar-Maker.


 * The Jiralhanae homeworld is erroneously called Oth Sonin in one reference. The novel previously identifies the planet correctly as Doisac; Oth Sonin is the name of Doisac's star system.


 * It is stated that Bal'Tol 'Xellus' "heart sank at the sight". This idiom is out of place as the Sangheili have two hearts, something that is acknowledged several times in the novel.


 * The Refuge is described inconsistently; in the first description, the eco level's "ceiling" is said to be convex and then concave in all subsequent descriptions.


 * External


 * Throughout the novel, the Ages of the Covenant's history are referenced as if each of the nine named ages were a singular and unique span of time. In previous fiction the Covenant age system has been established as being non-sequential, with each age gaining one of nine existing names according to major events that occurred in that age. For example, the Ninth Age of Reclamation (the period of the Human-Covenant War) is referred to simply as the "Age of Reclamation". There is implied to have been only a single "Age of Conversion" during which species were incorporated into the Covenant instead of multiple numbered ages with that name.


 * One description suggests High Charity still maintains a translucent atmospheric shield in lieu of its solid dome as of 2552, giving individuals in the city a view of the space outside much like at the time the station was still under construction. All depictions of the city-station in the modern era show the dome as being entirely opaque with no view outside.

Halo: Nightfall

 * Internal
 * Michael Horrigan remarks that Alpha Shard has a surface area of 96 km2. Based on Installation 04's established surface width of 318 kilometers and the fragment's length and curvature, the shard's surface area would be hundreds of thousands of square kilometers.


 * Jameson Locke implies that the HAVOK tactical nuclear weapon has a blast radius of 100 kilometers. The screen on the device later specifies that the weapon causes complete destruction within seven kilometers, and light damage for 44 kilometers. Despite this, the fireball from the same warhead completely overwhelms Alpha Shard's width of 318 kilometers.


 * The identification patch on Randall Aiken's uniform shows his blood type to be O+, though his service file seen on Jameson Locke data pad lists Aiken's blood type as AB-. This is likely a production oversight.

Halo: New Blood

 * External
 * Narrator Edward Buck states that Mickey "sounded as grim as a medic telling a soldier that the only good thing about him bleeding out on the battlefield was that his cancer wouldn't get him first." In Midnight in the Heart of Midlothian, cancer is described as a disease rarely seen since the 22nd century, and that it had become so uncommon that Michael Baird had never even heard of it until he was diagnosed. Cancer is also described as "easy to treat" with 26th century medicine. It is therefore unlikely that Buck would use cancer as a trivial example of a deadly disease.

Halo: Hunters in the Dark

 * External
 * It is stated that systems on Installation 07 control the "shifting of tectonic plates." As seen in Halo 3 and Halo: Primordium, the Halos have no tectonic plates as the ground is only several dozen meters thick, with solid foundational material underneath sculpted to create natural-looking terrain.


 * The elevator leading to the central chamber of the Ark's Citadel is said to descend from the antechamber into the structure's main room. In Halo 3, the same elevator ascends into the main room.

Hunt the Truth

 * External
 * Benjamin Giraud discovers an array capable of superluminal communications in a pre-Human-Covenant War ONI facility on Bliss, when according to Halo: Contact Harvest messages carried aboard starships were humanity's only means of FTL communication as of 2525 and in Halo: Ghosts of Onyx, the slipspace COM launcher was still the only way of delivering messages without a courier ship as of early 2551. While the array is eventually revealed to be a post-war creation created by ONI to trap Ben, he does not find its surprisingly advanced technology to be out of the ordinary.

Halo: Last Light

 * Internal
 * Frederic-104 estimates that Veta Lopis is "about half" his height without armor. This is unlikely, as this would make her only around 108 centimeters tall.


 * External
 * Olivia-G291 is consistently called by the nickname "'Livi". It is stated in both Ghosts of Onyx and Glasslands that she is nicknamed "O" because of her skill in stealth; she is considered "as whisper quiet as her vowel namesake."
 * When describing the history of her creation, Intrepid Eye claims that the Jat-Krula defensive sphere was constructed by the Builders after the Flood's re-emergence and the Warrior-Servants' first delaying actions to contain the parasite. According to Halo: Silentium, the Jat-Krula was already in existence over half a million years before the Ur-Didact was born.
 * In an attempt to silence Veta Lopis, Intrepid Eye seizes control of Fred-104's Mjolnir armor and attempts to kill her. However, in Halo: The Fall of Reach, Dr. Halsey assures John-117 that an AI (in this case Cortana) cannot control Mjolnir, explaining that while Cortana could increase his reaction time by translating the impulses in his motor cortex directly into motion, she couldn't make him send those impulses.
 * As a more advanced Forerunner AI, Intrepid Eye may not be subject to the same restrictions that human AIs have. Intrepid's measure of control also seems to be restrained to the armor itself, as Fred's mind remains his own and fights against her, suggesting she is projecting her own version of neural impulses into Mjolnir rather than making Fred send them. This is supported by Intrepid's previous lack of control when the armor is empty, as the AI finds she cannot move the armor when there is no neural interface plugged into it.
 * During the attempt to escape the Montero Cave System, it is claimed that Olivia-G291 was just as blind as Veta Lopis without the aid of her SPI helmet. However, this is contradictory to the augmentation that all Spartan-IIIs were given, which not only boosts vision during the dark but overall vision as well.
 * As the section is from Lopis' point of view and ostensibly describes her thought process, it is possible to regard this as an example of unreliable narration, with Lopis being unaware of the Spartans' augmented vision. However, nothing in the narrative is shown to contradict her assumption.

Halo: The Fall of Reach - The Animated Series

 * Internal
 * At least three Spartan-II candidates are depicted dying early in the training. Halsey's narration refers to this (in an uncharacteristically dismissive manner) as "removing the chaff from the wheat". All previous canon sources explicitly state that all seventy-five trainees survived until the augmentations. Nevertheless, following the SPARTAN-II augmentation procedures Halsey explicitly states that 27 children died, representing 36 percent of the candidates, math which holds true only if all 75 underwent the procedures.


 * External

Like Halo: Fall of Reach, the Animated Series departs from the source novel in numerous instances, with many liberties taken to better suit the medium. As it is not a particularly strict adaptation of the novel, one may regard it as an alternate interpretation of the original story, as opposed to an unintentionally contradictory narrative or a retcon. For a list of differences between the novel and the animated adaptation, see here.

Halo 5: Guardians

 * External
 * In the trailers A Hero Falls and The Hunt Begins (which are shown to be canonical by their inclusion in Hunt the Truth ), John and Blue Team are depicted as on the ground when the Guardian of Meridian emerged, running to reach it while avoiding a collapsing city's debris. In the game, Blue Team was already aboard the Guardian before it awakened.
 * This could relate to the fact that there were earthquakes while Osiris was inside the mines, giving a sense the Guardian was waking during that instead. As the main body of the Guardian was not shown in the trailers, it can be assumed the main body did not rise till after Blue Team entered. The fact Blue Team entered a portal at Apogee Station supports the journey they took.
 * Most of the marketing was misleading in general as All Hail and The Cost ads have no relevance to the story.

Halo: Shadow of Intent

 * External
 * San'Shyuum are said to lack earlobes, with their ear-analogs being just holes on the sides of their heads. However, in the remastered cutscenes of Halo 2: Anniversary, the wattles of San'Shyuum are depicted as long earlobes.
 * The prototype Halo that is tested on Sangheili prisoners annihilates them entirely, leaving no bodies or even trace particles. According to The Forerunner Saga, the Halo effect merely destroys an organism's nervous system but leaves the bodies intact, requiring the use of solute in the atmosphere to disintegrate the dead bodies thereafter.
 * It is possible that, being a prototype Halo, that specific weapon was designed to annihilate without use of a solute.
 * Prelate Tem'Bhetek wields an arm shield made of hard light. According to the Minister of Discovery, the Covenant had never learned to reverse-engineer hard light technology by the time of High Charity's fall to the Flood.

Lessons Learned

 * External
 * Jun-A266 is referred to as having been a member of Beta Company alongside Tom and Lucy before being pulled out for another operation. However, all prior sources depict Jun as being a member of Alpha Company.  Strangely, Lessons Learned actually mentions Jun's full Spartan tag, in which the "A" indicates Alpha Company, in the sentence immediately before he is mistakenly identified as being from Beta Company.
 * The narration mentions Tom and Lucy "joining Blue Team to recover an ancient AI on the hostile colony of Gao." Though this is not technically inaccurate, the wording is peculiar, as it implies the pair joined Blue Team specifically for Operation: JOVIAN WHISTLE. In fact, Tom and Lucy had already been part of Blue Team for a few months at that point.
 * It is stated that Tom and Lucy had "gone through countless hours in zero-G, both in training and in combat, but they'd usually been wearing Mjolnir armor while doing so." It is improbable that Tom would regard the use of Mjolnir armor a "usual" occurrence in training or combat situations, as he would have been far more used to using SPI armor for most of his career. While it is likely that he and Lucy were trained to wear Mjolnir armor following their assignment to the Spartan branch, the story implies that they had been serving solely as instructors following the events of Halo: Last Light, and does not otherwise mention them participating in combat after the mission on Gao, during which they still wore SPI armor.

Breaking Strain

 * External
 * Captain Darren Leone knows that Kevin-A282 is a member of SPARTAN-III Alpha Company. By virtue of Kevin's service with Alpha Company, Leone is shown to be aware that Kevin "... had seen some of the worst of the war with the Covenant, on colonies like Kholo and Meridian, even Sigma Octanus IV not long ago." Given the top-secret nature of the SPARTAN-III program (which was never declassified during the war) it is exceedingly unlikely that Leone (who prior to the events of the story was merely the helmsman on a cargo tender) would be aware of the Spartan-IIIs as a distinct formation from the publicly avowed Spartan-IIs at all, let alone that he would be aware of their internal organization and operational history. Furthermore, Leone's reflection on Kevin's past service implies the whole of Alpha Company (rather than just Kevin and his team) had fought in the aforementioned battles. In fact, the vast majority of Alpha Company had been killed during Operation: PROMETHEUS in 2537, two years before the Battle of Kholo and well over a decade before the conflicts at Meridian and Sigma Octanus IV. Kevin is a "cat 2" deployed outside his original company; though several "cat 2s" from Alpha Company remained active after Operation: PROMETHEUS, referencing the company as if it had, as a whole, survived as late as the Battle of Sigma Octanus IV in July 2552 is highly erroneous. Leone's point-of-view narration also notes Alpha Company as "one of the longest-serving SPARTAN-III units." Only two comparable units, Beta and Gamma Companies, were ever founded, so such a comparison holds little weight.

Promises to Keep

 * External
 * The Engineers are established as a rate composed of members of the Forerunner species. Previously mentioned only once, in Halo: Cryptum, context in that novel indicated that the "Engineers" actually referred to the Huragok, not a class of Forerunners; the author, Greg Bear, later confirmed this in a forum post.
 * It is stated that the Forerunners did not return to the Capital between the Fate of Maethrillian and their expedition to restore the Domain over a century after the Halos had been fired. However, Halo: Silentium states that the Forerunners rescued survivors from deep within the Capital after Mendicant Bias' attack, and that the Capital system was overwhelmed by the Flood only later in the war, at which point the Council was moved to the greater Ark.

Rossbach's World

 * External
 * In the short story, Rossbach's world, Serin Osman remembers that her abductor was a male ONI agent. However, in Halo: Mortal Dictata, it is stated that the agent was a female.

Halo Wars 2

 * Internal
 * Various assets designed by Creative Assembly (seen on in-game models, unit cameo icons, menu and Blitz card art, and the main menu model diorama) differ from their counterparts in Blur Studios' pre-rendered cutscenes. For example, Creative Assembly's Marines (gameplay) wear armor that resembles the post-war version introduced in Halo 4 and wield MA37 assault rifles which is canonically standard-issue for the Army rather than the Marine Corps' MA5; whereas Blur's Marines (pre-rendered cutscenes) wear the armor model from Blur's cutscenes in the original Halo Wars, and they use Marine-issue weapons such as the BR55 battle rifle. Creative Assembly's interpretation of Spartan Red Team's armor resembles a hybrid of the Mark IV, Mark V, and Mark VI; in cutscenes, mission briefings, and in-game communications, they wear their armor from the previous game. Notably, Douglas-042 is consistently represented during communications by a headshot of his original helmet throughout the game, even though it is destroyed near the beginning of the campaign.
 * The disparity in the Marines' armor may be due Isabel modernizing the ' s production facilities and design templates. It is possible that some Marines assigned to the ship (those seen in cutscenes) continued to wear the older model. The real world reason is likely due to the two separate teams (Blur and Creative Assembly) starting their versions of Marines at different times.
 * The Spartans of Red Team canonically upgraded their suits using modifications by Serina and Isabel as well as by incorporating Mjolnir GEN2 components sourced from the Ark. 343 Industries writer Jeff Easterling has stated that the disconnect between Creative Assembly's and Blur's Mjolnir designs is due to resource constraints.
 * Alice-130 is shown issuing orders to Marines in the menu art for the level "Hold the Line", even though the mission is actually led by Douglas-042.
 * According to its Phoenix Log entry, the EV-44 Nightingale was developed very recently as of 2559, and it is due to the craft's relatively simple structure that its design template could be adapted to Spirit of Fire ' s older factory lines. In the campaign mission "The Signal", however, Douglas-042 (who has been in cryo-sleep since 2531) recognizes the craft and is aware of its medical response role before contact with the Ark's UNSC presence is made. Furthermore, DLC for the game later revealed that Spirit of Fire ' s shipboard AI, Serina, designed a theoretical variant of the Nightingale, the ZAV-48 Frostraven, at some point before her final dispensation in 2537.


 * External
 * Jerome-092 is shown carrying Isabel aboard his Mark IV armor at various points in the campaign. While supported by Jerome's armor, Isabel is shown to be aware of her surroundings and able to function normally. However, the ability for Mjolnir armor to support an AI was not introduced until the second generation of the Mark V (the first model to feature the necessary memory-processing superconductor layer) entered service in August 2552.
 * Although the Spartans' suits were canonically upgraded, which may explain Jerome's suit's ability to support Isabel later in the game, she is nonetheless shown to function normally during the escape from the Henry Lamb Research Outpost, which occurs before Jerome's armor could have been outfitted with the necessary superconducting layer.

Halo: Meridian Divide

 * External
 * Captain Delletorre says that "all Spartan-IIIs have their genetic code modified as part of their treatment." Although Spartans are frequently referred to as genetically-augmented in external media, this is actually a common misconception. All previous canon consistently states that Spartan-II and Spartan-III candidates were only subjected to genetic screening to determine their suitability before being subjected to biochemical and biomechanical augmentations in Project ASTER and Project CHRYSANTHEMUM, respectively. It was not until the SPARTAN-IV program and Project ORCHID that Spartans were subjected to gene therapy.

Ancillary material

 * According to complementary fiction released in the Halo Wars: Official Strategy Guide, the Covenant had discovered Shield World 0459 prior to the events of Halo Wars. The Halo Waypoint video series "The Halo Wars Story Retold" instead claims that the Covenant discovered the shield world from data gathered at the Forerunner ruins on Arcadia. The version given in the game guide (ostensibly written by the game's writers as background fiction to flesh out the characters) is seemingly supported by the in-game story: the first scene showing the Covenant on the shield world does not give any indication that the shield world is a recent discovery, only serving as the backdrop for the Prophet of Regret and the Arbiter's conversation about the events on Harvest and Arcadia.


 * In the second Data Drop, Vice Admiral Stanforth states that several cities on Sigma Octanus IV (Caracas, Huiren, Côte d'Azur, Silma and Enfield) were destroyed during the battle for the planet. Halo: The Fall of Reach explicitly states that most of the planet was spared with fighting only in and around Côte d'Azur.


 * According to Halo 4: The Essential Visual Guide and, Carlo Hoya was born on Asmara in 2533. However, data pad 14 in Halo: Reach indicates that Asmara had been glassed by the end of 2529.


 * Halo: Official Spartan Field Manual incorrectly lists the Battle of Installation 00 as taking place in November, 2552, when the battle actually happened on December 11, 2552.

Multiple sources
Conflicts which involve more than two sources are listed here.


 * All pertinent media released since 2009 state that 25 of the 28 active Spartan-IIs still assigned to NAVSPECWEAP (from an initial unit of 33) were summoned to Reach for Operation: RED FLAG. The three absent Spartans were Gray Team, who had been out of contact since 2551.


 * Two Spartans (including Oscar-129) committed suicide after escaping the program in mid-2525. Samuel-034 became the first Spartan to be killed in action in November 2525. At some point in the early years of the war, Jerome-092, Douglas-042, and Alice-130 (all of whom had "washed out" by failing to adapt to their augmentations) were retrained, re-augmented, and placed into active service, bringing the total number of active Spartan-IIs back to 33. Daisy-023 and an unidentified Spartan-II were killed in early 2531. Jerome, Douglas, and Alice went missing in action in February 2531; they were stranded outside UEG space aboard, which was declared lost with all hands in 2534. In November 2531, Kurt-051 was abducted by the Office of Naval Intelligence to lead the SPARTAN-III program. Randall-037 went MIA on Vodin in 2532 and secretly returned to civilian life, though Dr. Halsey considered him truly missing.


 * Cal-141 was killed on Heian in the early 2540s. Three Spartans were killed in action between 2542 and August 29, 2552: Sheila-065 died on Miridem in 2544, while Solomon-069 and Arthur-079 were killed during Operation: WARM BLANKET shortly thereafter. Another Spartan was too heavily wounded to continue active duty in this time frame. Jorge-052 fought during the Fall of Reach, though he served with Army SPECWAR's NOBLE Team rather than being recalled for Operation: RED FLAG; however, it is possible that Jorge being the wounded Spartan was a cover story for his reassignment to NOBLE Team. By this count, no more than 20 Spartan-IIs could have been present for Operation: RED FLAG, with the possibility that Jorge and the wounded Spartan are synonymous bringing the number to 21.


 * In her journal, Dr. Catherine Halsey expressed her hope that Kirk-018 and René-081, two of the twelve crippled "washouts", could be rehabilitated and returned to active duty; she further noted that experimental rehabilitation protocols were in development for 80% of the washouts and that AIs predicted a total survival rate as high as 50%. Jerome-092, Douglas-042, and Alice-130 were eventually rehabilitated and placed on active duty by February 2531. Soren-066 escaped the program in 2526, having unwittingly joined the Insurrectionist cause; Halsey refused to bring him back into the fold against his will and he presumably died afterward. Ralph-103 was discharged due to psychological problems and his augmentations were curtailed; he later joined the Marine Corps and was killed in 2531. The wheelchair-bound Fhajad-084 became an ONI data analyst. Maria-062 retired sometime before October 2552, though she was still capable of using Mjolnir powered armor. Cassandra-075 was still undergoing skin grafts as of October 2552. Musa-096 also became wheelchair-bound and was responsible for developing the SPARTAN-IV program by January 2553. In addition to Jerome, Douglas, and Alice, this leaves three washouts who were potentially rehabilitated and returned to active duty, which could increase the number of Spartans at Reach to as many as 24.
 * Dr. Halsey refused to allow invasive autopsies on the deceased Spartan candidates' bodies and arranged a closed-casket funeral; the coffins were empty and the bodies were actually placed in cryonic storage. She feared what ONI would do with the candidates' cadavers, suspecting that they would form their own, secret Spartan unit; indeed, this is presumably how the four-member Black Team came under ONI's command. Given that Halsey resurrected Linda-058 from clinical death with the rather limited facilities aboard the, it is possible, though very unlikely, that the Spartan-IIs' numbers were bolstered by some of their once-clinically deceased comrades.
 * Although the other Spartan candidates were told that Serin-019 had died, in reality she survived in spite of rejecting most of the augmentations. She was withdrawn from the program before the washouts' closed-casket funeral and was later reassigned to the Office of Naval Intelligence as CINCONI Margaret Parangosky's personal attache. It is possible that other Spartans (such as the aforementioned Black Team) were likewise falsely reported as dead.
 * i love bees depicts a second class of Spartan-IIs that was launched around 2537, though this class has not been referenced in subsequent media. Assuming the second class is still canonical, the original Spartans' numbers may have been bolstered with later Spartan-IIs.


 * In Halo: The Flood, the D77-TC Pelican's operational capacity is said to support a pilot, a copilot, a crew chief, and 12 passengers in the troop bay. According to the Halo: Combat Evolved strategy guide, the Pelican can operate with three crew members, ten seated passengers, and five standing passengers. In Halo: The Flood, Pelican Charlie 217 carries 30 Sangheili in the troop bay in addition to the human pilot and another Sangheili in the cockpit. In Halo: First Strike, Pelican Bravo 001 carries 22 Spartans, though the Spartans had removed all unnecessary equipment from the troop bay, including the seats, and were packed nearly shoulder-to-shoulder in the troop bay; Halo: Fall of Reach - Invasion, which rather loosely adapts the story of Red Team's insertion from First Strike, shows that the Pelican had an expanded bay and far more massive overall than normal Pelicans. Pelicans seen in-game feature ten seats and could easily accommodate around ten more standing passengers.


 * In many sources, such as Halo: Last Light and Halo Wars 2, Spartan-IIs and Spartan-IIIs are regularly addressed by their first names by fellow UNSC personnel and even civilians. It is stated in Halo: The Flood that the Spartan-IIs' names are not common knowledge even within the military. Throughout Eric Nylund's novels the Spartan-IIs and Spartan-IIIs alike are instead most commonly addressed only as "SPARTAN" followed by their numeric tag in professional contexts; references to the Spartans in the games follow the same format, along with the use of the phonetic call sign "Sierra" in some cases.


 * The extent of the capabilities of Forerunner slipspace portals has been depicted inconsistently across different sources, with several newer works introducing portals capable of transporting individuals across interstellar distances without the use of a starship. In Halo: The Thursday War, the first source to depict this type of portal, Evan Phillips states that it is common for Forerunner portals to displace individuals to different planets. Later in the novel, a teleporter on Trevelyan propels Jul 'Mdama over a distance of many lightyears, all the way to the Sangheili colony of Hesduros. Individual translocation across interstellar distances (or the broader implications of such technology) is never acknowledged in any prior source. Given that the teleportation grids on the Halo rings, for example, are exclusively local systems (the teleportation grid on Installation 04 does not extend even to the nearby Threshold), logic would dictate that individual teleportation does not operate on an interstellar scale and that a starship is required to access the larger-scale slipspace portals due to the dangers of long-term unshielded exposure to slipspace. In Halo: Ghosts of Onyx, comparatively short-range translocation across Onyx causes severe nausea and disorientation to the characters; such effects are nowhere to be seen with later depictions of portal-based translocation. In Ghosts of Onyx, it is also noted that slipspace travel to another star system would have taken some amount of time rather than being instantaneous, a fact that enables Dr. Halsey to deduce the survivors from Onyx never traveled across an interstellar distance when they entered the shield world in the core of the planet.


 * Individuals traveling interstellar distances instantaneously via portals are later featured in Halo: Escalation ' s "The Next 72 Hours" story arc and Halo: Spartan Strike, suggesting that this may represent a universal retcon regarding the Forerunners' translocation capabilities. Alternatively, it is possible that interstellar teleportation was possible only to a limited extent or under specific circumstances, but not regularly practiced due to possible issues with safety or reliability. Notably, all known instances of individual portal transit are based on Forerunner military installations; shield worlds and Halos, while the portals in Spartan Strike are related to the special artifact known as the Conduit.


 * In The Package and Halo 4: Forward Unto Dawn, Kelly-087 speaks with a General American accent. In Halo: The Fall of Reach - The Animated Series and Halo 5: Guardians, she speaks with a British accent. According to 343 Industries, the latter should be considered the definitive portrayal of the character, with the prior ones regarded as artistic license.


 * In Halo: First Strike, it is clearly stated that Eridanus II was a colony destroyed by the Covenant on 2530, and this fact is referenced various times in the novel. In Halo: Warfleet, however, it is stated that "The planet's urban areas were destroyed at the end of the Covenant War, but enough population and infrastructure survived to ensure Eridanus II was selected for priority redevelopment". Even though it's possible that the Covenant gave back the colony at some point, just to return at a later date and glass it a second time, this is probably just a mistake.

Written works vs. visual media

 * According to Halo: The Fall of Reach and First Strike, the Spartan-IIs wore identical Mjolnir armor which lacked any identifying features, making it nearly impossible for an outsider to tell them apart; Dr. Halsey distinguished the Spartans only by the subtleties of their movement. However, in later visual media they are shown displaying their numeric tags on their armor and wearing specialized Mjolnir variants. At least five Spartan-IIs (Jerome, Douglas, Alice, Cal, and Kelly) even had pinup art painted on their Mark IV suits.
 * Such distinction is all but necessary in a visual medium, as making the Spartans superficially identical would no doubt confuse the audience. While the Spartans could distinguish one another by body language, having their tags displayed could benefit any non-Spartan personnel they served alongside. The reason behind the Spartans' use of armor variants is more obvious: forgoing their use would be out of character, particularly for specialists who could make use of MOS-intended models. From a production standpoint, this is because The Fall of Reach and First Strike were released before Halo 3 introduced the concept of purpose-built armor permutations.


 * In Eric Nylund's books Dr. Halsey is often said to wear glasses, habitually pushing them up her nose. In each of her visual appearances (with the exception of Homecoming) Halsey does not wear glasses, while the Kilo-Five Trilogy simply makes no mention of them. The novels also frequently describe Halsey as having her hair tied to a bun, which is never portrayed in visual media; she is instead most often depicted as sporting a hairstyle roughly similar to that of Cortana in Halo 3.


 * In all of its visual appearances slipstream space is depicted as having some form of visible effect to it, often a blue-tinted tunnel. In all written media slipspace is established as being a nonvisible inky void, barring the anomalous slipspace pocket generated by the Forerunner crystal in Halo: First Strike which caused a number of ships to be trapped in a slipspace bubble resembling blue fog. Presumably, the visual depictions of slipspace are concessions to visually convey the movement of ships traveling in the alternate domain.


 * In the novels, it is common practice within the UNSC for individuals to enter cryosleep naked due to the risk of intense blistering and pain caused by clothing adhering to the skin.  In Halo Wars, The Package and Halo 4: Forward Unto Dawn, individuals are shown entering cryo fully clothed. Forward Unto Dawn introduces dedicated skintight bodysuits for use by personnel in cryo; it is possible that the atypical clothing worn by Dr. Halsey in The Package is meant to function in a similar way, although Ellen Anders is wearing her normal civilian clothes when entering cryo in Halo Wars. In any case, the omission of nudity from scenes involving cryosleep is obviously a case of artistic license for content rating reasons.


 * The size of the explosions produced by HAVOK tactical nuclear weapons varies considerably throughout Halo media. For individual examples, see here.