UPDATE: Also, someone emailed Jonas Goldberg his memories of a proportional IBM typewriter circa 1971-1974 at Patrick AFB. Nobody wanted to use it because backspacing required a "en" chart.
Which would make it the perfect typewriter for Killian to dash off memos to himself about various subjects.
And CYA has been a military slang term since the '50s.
SECOND UPDATE: The Washington Post has the forgery story on the front page. Someone at CBS spilled on the source who authenticated the content of the memos: Major General Bobby Hodges, who's named in the memos.