1841 $2.50 Liberty Head
The 1841 $2.50 Liberty Head was originally believed to be a proof-only coin. However, there are too many specimens as compared to mintages of other proof quarter eagles during the same period, which are typically less than 5. There are at least 12 and possibly 15 1841's known to exist, and only a few are undoubtedly proofs. Most are definitely circulated (which proofs are not). All the known specimens of the 1841 were apparently struck from the same dies, which would normally indicate they were all proofs. But since some are not proof quality, and there is no record of a non-proof mintage, the mystery remains.