CYA has been used for a long time. Certainly since before the '70's.
Perhaps CYA was used, but in the military culture I joined in 1974 it was an insult, indicating that the person concerned only cared about himself.
No commander with half a brain would write a memo that is literally a CYA memo. It is a ticking time bomb, waiting to go off. It is written evidence that the commander knew he was doing something improper, illegal, unauthroized or in contravention of military orders and procedures and went ahead and did it anyway. If it ever sees the light of day the commander is dead.
Besides no fighter jockey thinks that way anyway. In addition to the form proving a fogery, the content proves a forgery.