So I bought a few of the 50th anniversary proof sets and was comparing them. One quarter in particular has an obverse with completely frosted "Quarter Dollar", IGWT, "Liberty" and "United States of America," while the others are all nice and shiny. The only other reverse proofs I have collected are from the March of Dimes sets, so I don't know much about them. Is this just an undesirable characteristic or is it considered a sort of variety or error?