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."
