Character mistake: When Moss is arguing with the border guard at the Eagle Pass international bridge, he claims that he is a veteran of the "12th Infantry Battalion." There has never been such a thing as the 12th Infantry Battalion in either the Army or the Marines. Rather, they are based on a structure of 3-4 battalions per numbered regiment (i.e., 1st Battalion, 3rd Infantry Regiment/2nd Battalion, 5th Marine Regiment, etc). The film takes this seriously, as the guard, a veteran himself, buys Moss' story.
Suggested correction: He might have meant 12th Infantry Regiment. From Wikipedia: "Three 12th Infantry battalions deployed to South Vietnam with the 4th Division from August through October 1966."
If he said "battalion" but meant "regiment", then it's still a valid mistake for saying it wrong and being believed.
Regiments have not existed as functional units in the US Army since shortly after Korea; they are simply historic names associated with various battalions. Marine battalions are not numbered higher than 4 in any regiment, and in any case do not carry an explicit designation of "infantry."
Character mistake: In one scene, Ashley looks into Mr. Turner's yard with binoculars. She looks through the large glass circles. That would result in seeing everything smaller. If you want to see everything bigger, you are supposed to look through the small glass circles.
Character mistake: Jonesy says he read about Amber going to West Point. She was a Marine, and not in the Army, which is what West Point is for.
Character mistake: When Johnny Blaze plans on jumping the football field he says he is jumping field goal to field goal. The movie says multiple times he is jumping 300 feet. End zone to end zone is 300 feet. Field goal post to field goal post is 360 feet.
Character mistake: The endotracheal tube (breathing tube) was not secured to the patient. It is standard practice to secure this tube to the patient in order to keep it in place.
Character mistake: The coroner examining Jennifer Toland's body reports that her fingers were cut off first, then the metacarpals (palm bones) were removed later. Given that when she is found her entire limb is missing up to her mid-forearm, how could he possibly tell not only that the missing part was not all removed at once, but which bits were cut off in which order?
Character mistake: Jungle Julia refers several times to Dave Dee, Dozy, Beaky, Mitch and Tich, instead of Mick and Tich.
Character mistake: When LT. Col. Robert Neville's wife fails the eye scan and he's ordering the soldiers to scan her again, the soldier that escorts them to the scan point, and later to the helicopter mistakenly uses Will Smith's real last name. You can faintly here him identifying LT. Col. Robert Neville to another soldier as LT. Col. Robert Smith.
Character mistake: When Donnie (spotter) is giving Swagger ranges to fire, he doesn't tell Swagger what hold to use.
Character mistake: When Mr. Brooks and Marshall hack into the police database and are looking at detective Tracy Atwood's financial records there is a screenshot of the computer screen showing some very terrible spelling.
Character mistake: Alice shoots the henchmen, the black officer is attempting pull a gun from his shoe but in closeup his leg is white, then back. (01:06:25)
Character mistake: Nikolai is driving Anna home after the bike went kaputt in the rain, outside the restaurant. Anna towards the end tells him to "take the next right." Both Naomi Watts and Viggo Mortensen are looking left, and keep their eyes there. (00:28:25)
Character mistake: Sam says that Archibald Witwicky explored the Arctic Circle in 1897. But when Frenzy finds the article, it is dated 1895.
Character mistake: Roy says, "He thinks the wounds look self inflicted." But the doctor who said that was a female.
Character mistake: As Jason reads the Guardian Newspaper, he finds an article about himself entitled, "Who is Jason Bourne?" The caption for the article reads, "His code name is Jason Bourne, but he had many identities, each one seemingly more deadly then the next," instead of "more deadly than the next." (00:12:50)