I agree it isn't an RPM, but why can't it be one? They were still hand punching the mint marks in 1982. Is it something to do with Philly coins? I noticed there are no quarters or nickels (other than war nickels) that are P/P RPMs. Is there a reason behind this?
Sorry, got my dates wrong. This from Wexler: In 1990 and 1991 the Mint began applying the mint mark to the master die for circulation strike coins. After 1994 the mint mark was placed on the master design. http://doubleddie.com/58201.html