This does not look like an error to me. I don't think it's something that happened during the production of the coin. Rather it looks like after the coin left the mint and went to circulation, somebody did some kind of milling or tapping on it which caused the metal from top and bottom to bend and flow over the central portion. I've seen things like this before. It doesn't add value to a coin in fact it's considered damage.
📋 Item Submitted
1991qua with edge error
M
Marc's Expert Appraisal
ANA-Certified Numismatist · Hudson Valley Numismatics
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