Sorry, but those aren't rpms. What you are seeing is damage that happens a lot around the mint mark. The zinc becomes corroded. That's on the second one. The 80D appears to just be a hit to the mintmark.
lol someday enamel i will post one and you will say yep now thats a keeper. i was more unsure of the 92 because the mint mark was on top but now that you said corrosion i would agree after digging them nasty zincolns it makes sense as always thanks