
1989 was the last year of the hand punched dies happened. Starting in 1990, the mint marks are part of the design on the master die. So all coins from that mint will have the Samantha mark, same location and thus took RPMs out of the equation. If the mint marks are doubled after that it would be from MD or a doubled die. A lot of mint marks after that year are affected with die wear. But a few dies do have DDOs on the date and mint mark area, but not very often.