Dan Rather's published a document he says was created in August, 1973.
http://www.cbsnews.com/htdocs/pdf/BushGuardaugust18.pdf
A lot of people who know a lot more about the military, type styles, kerning, superscripts, etc. have commented on these, and a large number of people have concluded they are fakes.
I have to question something more basic - the subject line of the above document - it's simply "CYA." Was CYA used as an acronym in 1973? I don't believe so. Cover your ass was certainly used, but the three-letter-acronym craze had not begun in 1973. I've searched through several slang books, but CYA is only dated as "late 1900s" which doesn't tell us much.
A search on questia.com turns up the phrase a large number of times, but none are before 1994 - and the earlier examples explain it parenthetically. That's a sign, to me, CYA was relatively recent in 1994.
I've also checked with a couple of writer friends, and they concur - CYA was probably not used in 1973.