I don’t know of any listed 1978-D rpms, that doesn’t mean there aren’t any or a new one could be discovered. Your coin appears to have taken a hit on the mint mark.
I think you're looking too hard for errors, and you're just trying to convince yourself that every oddball coin is an error. Looking for errors among circulated coins, especially ones that are decades old and possibly subject to all kinds of mistreatment, won't get you anywhere. ~ Chris
