70's

I'm I reading this correctly? I have a pair of tanks they are about 6.9"x 19" tall about 22# Dot-3AA 2015 (moly with psi of 2015 -> 2216 with plus) HM 53 385 (Serial # ) (Norris stamp/N in diamond) 1N77 + (L inside C) made and tested by Norris on 1/1977 ) never hydroed again looks new inside...