In 1921, the U.S. Mint began making Silver Dollars again after a quiet period of seventeen years with none being made. Along with the regular strikes made for circulation, the Mint struck Proofs on the orders of Farran Zerbe and Henry Chapman. The Zerbe "Proofs" are more prooflike in comparison to the true Proofs of 1904 and earlier. The Chapman Proofs, however, are more convincing in appearance, but even they present a conundrum to the numismatic researcher. According to most reports, the original number of Proofs made for Chapman can be either 10 or 15. However, PCGS alone has certified 39 Chapman Proofs (as of October 2014). Even discounting for resubmissions, one must question the inordinately high number of survivors, a number that appears to exceed the original mintage. Either the Mint struck additional Proofs for someone else -- and that transaction was unrecorded -- or there is a problem with the die characteristics used to identify a Chapman Proof. I suspect the former.
Either way, the 1921 Chapman Proofs are very rare and highly desirable, mostly because of their stunning appearance. Many have been mishandled, thus they only grade out at the PR63 level, but at least two Gems exist (a PCGS PR65 and PR66). The PCGS PR66 last appeared at auction in 2000, when it sold for $60,375, perhaps half as much as it would bring today.
Superior 10/2000:3768, $60,375 - Sunset Hill Collection - Legend Rare Coin Auctions 12/2014:297, $123,375