I have a 1985, mint proof set. The Lincoln has turned 3/4's black; every other coin is mint state. Since the set was packaged at the San Fran mint, would the Lincoln be considered a "mint error"? Looking for interesting opinions.
You are correct sir. I should have posted pics. My rational, if it was packaged at the MINT it's their BAD.
When your coin was initially packaged, I assume it looked fine then. What happened over time, possible air leak is not a mint error. Just sloppy packaging materials. I have a proof set from 1988 and some of the coins have toned as well as a sort of broken S mint on the dime. It's still worth barely what I paid for it. So after 36 years my profit is 0 if I sell it. I could have sold it a while back for $5 but I didn't want to take the loss.
That is some weird toning. I've never seen anything like that in a proof set. Got a shot of the reverse?