The only Mintmark that wasn't present pre 1980 was Philadelphia (With the exception of the wartime nickels)
Because Reagan would have returned the dime to you if you had dropped it. Nixon would have kept it. Chris
The Susan B. Anthony dollar carried the P mintmark from its introduction in 1979. The P mintmark was added to all other Philadelphia nickel-alloy coins in 1980.
When the Suzies were introduced in 1979, they were criticized for their design, and people were always mistaking them for quarters because of their similar size, color, and reeding. When I wanted to spend one, I often had to show the recipient the reverse to show that it was actually ONE DOLLAR. They were issued in large numbers in 1979, but mintage figures slackened off dramatically in 1980 because no one was using them, and in 1981 they were only made for mint sets. Finally, the Mint threw in the towel and quit making them altogether in 1982.