I could be wrong but I'm pretty sure it would have happened if, say, the San Francisco mint shipped a die or dies to ,say, the Denver mint to use for production, in which case Denver would try and punch the D in over the S to make it their own die. Someone correct me if I'm wrong.
The coin did not originally get one mintmark and then another - the die did. So any coins struck by that die will have the overmintmark.
Forgive me my ignorance, but when these mistakes are made, do they KNOW it and just keep going? Miss part of their q c? No 'measure twice, cut once'? And, going back to the beginning of this thread, I do see the doubling in 'Liberty', but fail to pick up on what it is you are all seeing in the date (1909 , photo posted) Fascinating anyway.. thanks, Lucy
In the old days, mintmarks were added at Philadelphia where the dies were made. An S/D was a rather unusual mistake mede there.
A common variety...1900 O/CC...since dies were expensive to make, when CC mint closed down, they shipped the dies, in this case, to New Orleans.
Good explanation by Hobo. The only thing I could imagine the term "double die" to mean would be two dies.
These aren't errors. An error is from a production mistake on a single coin, and as such will be a unique occurrence. When something happens to the die such as with doubling or repunching, all coins created from that die will be a variety, not an error.
Double die doesn't mean anything. It's like one of those meaningless sayings like, "rama-lama-ding-dong" or "give peace a chance."