Does an "s" mint mark always mean that the coin was once part of a proof set? If a coin was once proof, but was spent and circulated it would obviously become "unproof", would it not?
after 1974 there all proof with an S. but the us mint made a 68-70-S nickles and 1968-1974-S cent's that are not proofs
S mint mark indicates the coin was minted at the San Francisco mint. Your second sentence is somewhat true...If indeed someone spent a proof coin...it would then be a "circulated" coin. This may happen on occasion...maybe a grandkid got into grandpa's coin collection and went to the convenience store....the clerk would probably snag it and add it to their collection.
Before 1975 the San Francisco Mint, mint mark(mm) 'S', produced coins for circulation as well as made proof coins. Since then, it took over minting only proof coins except in the early 1980's when it produced some cents and later some other coins. I think a proof coin is always a proof coin even if it somehow gets into circulation. Then its condition deteriorates and loses its grading status. But it was made and still is a proof coin, in my opinion. Wow, I said that!!! zg
Once a proof coin, always a proof coin. Proof refers to the method of production, not the condition. When a proof coin has defects, it is merely graded lower, just like a business strike. These proofs are commonly referred to as "impaired proofs", and may be issued grades lower than 60. For instance, it is perfectly acceptable to refer to a circulated proof coin as PF-40.
