I still have stuff I bought at Andy & Bax in Portland back in the late 60s/early 70s.
Bought a VN era field desk in late ‘70s (still have it on my porch)and found an addressed envelope behind a drawer, addressed to a lady.
Couldn’t tell the date without opening it (I did not) but I was there in ‘68/69 and decided I’d want it sent on.
Sent it in a larger envelope with a note so the recipient would be able to determine on her own to read it or not.
No word on the effect.