Pentagon was referring to the P.O. Box as letterhead.
It was in reference to one of the "FORGED FOUR" from CBS.
Not in reference to standard forms.
No sweat. It is interesting that the PO Box addy was the one given, I think, for Bush's unit. The forger grabbed that and translated it to letterhead. A perfunctory "fact check" would indicate authenticity, and lead a gullible news agency down the path.