Harper's Ferry OMM Or MD?

RPM and OMM have been impossible since 1990. Before 1990 the mintmarks were added to the die by hand and any slight movement would cause an RPM. Now mintmarks are added to the die the same way the design and lettering are added.

Someone else could probably explain that much better than I can.

Until the 1990 cents, the mint marks were placed on the die with a mint mark punch. These were hand done and could vary in locations/angles on the die. There is was also an issue with the mint marks have a spread between punches. Some minor, some major. But they ended that in 1990 with the mint marks being applied on the die as part of the design. We often get asked questions about some mint marks that look like a RPM. They are most often Die Deterioration. On some dies, there was a doubled die that did affect the mint mark. So after 1990 if they were actually showing doubling on the mint mark, they are actually doubled dies. I can only think of one examples so far that I know of where this happened.

This is the only one I know of, but hundreds of times it is usually always been Die Deterioration or machine damage on those mint marks.

As far as OMM (Over Mint Marks) that no longer can happen after 1990. (the mint mark is part of the design)