Heritage Auctions - Every circulation-strike issue from the inception of the
Morgan dollar series in 1878 through 1904 was accompanied by a small run of proofs, typically in the high hundreds of pieces. The year 1921, when
Morgan dollar output resumed for one last time using newly created hubs, was different in a number of ways, including the proof mintage.

The story goes that numismatic promoter and entrepreneur Farran Zerbe had "proofs made — some say 20, some 24, some 25, other 200, exact quantity not known — as a kind of consolation for his not being able to get the
Peace dollars into the public's hands during the calendar year 1921," according to Walter Breen's Proof Encyclopedia. The status of the so-called Zerbe proofs, which are recognized at PCGS and NGC, is somewhat controversial. However, there is no denying the proof origin of these Chapman proofs, which were ordered by dealer Henry Chapman after hearing about the Zerbe coinage. According to Breen (1988), "Chapman went to Mint Engraver George Morgan, and obtained 10 proofs of much higher quality, thus creating one of the major rarities of this century with the
Morgan dollars' last gasp." It should be noted that Breen cites a mintage of 12 Chapman proofs in his Proof Encyclopedia.
The PCGS and NGC certification totals are almost certainly inflated, with the former reporting 46 submissions and the latter showing 23 grading events. Dave Bowers notes in his Guide Book of
Morgan silver dollars: "I have only ever seen a handful in 65 years that I would call mirrored Chapman proofs."
See the listing on Heritage.