The 1876-CC Proof Dime is a very rare and interesting coin that first appeared in a 1983 Stack's sale. There, Stack's called it a "Choice Brilliant Proof" and noted: "It is not listed in any of the standard reference books such as 'Breen's Encyclopedia' or the 'Standard Catalogue' of years ago." This indicates that experts knew of no Proof 1876-CC Dimes prior to 1983. Inexplicably, Breen did not mention the coin in his 1988 "Encyclopedia." This particular coin resurfaced in a January 2008 Superior auction, where it was given a full page treatment as one of the highlights of the sale. The Superior description referenced an example "believed" to be in the National Numismatic Collection at the Smithsonian Institution, plus four examples certified as specimens by another grading service. Certainly, this is one of the rarest proof coins of the late 1800's.
PCGS has recognized only two Branch Mint Proof examples of this date (both of which are listed in the Condition Census above). Any potential candidates should be sent in for certification to determine their true status.
Researchers have been unable to determine the reason why this special coin was struck.