For several different years, some proof Roosevelt Dimes from the San Francisco Mint were struck without the “S” mintmark. For each occurrence, the “No S” Proof Roosevelt Dimes are rare. In a few situations, the coins are significant rarities with only a handful known to exist.
The 1968 “No S” Proof Roosevelt Dime was the first situation. Responsibility for making proof dies rested with the Philadelphia Mint and production took place at the San Francisco Mint. At least one die was sent from Philadelphia lacking the “S” mint mark. A small number of dimes were struck with the die and released before the mistake was discovered. Approximately 12-14 examples are known in all grades. One of these, graded by PCGS as PR68 Cameo, sold for an astonishing $48,865 in September 2006.
Two years later in 1970, more proof Roosevelt Dimes were struck without a mint mark. This time production from an entire die pair was released before discovery, resulting in an approximate mintage of 2,200 of the 1970 “No S” Proof Roosevelt Dimes.
The 1975 “No S” Proof Roosevelt Dime emerged as the rarest of this error type. An extremely small number of proof coins missing the mint mark were released. The coins were so rare that they were not discovered until 1978 when two examples surfaced. These coins are now considered one of the major rarities of the 20th century with an estimated 2 to 5 pieces known. No examples have been graded by either PCGS or NGC.
One more time in 1983, proof dimes were minted without the “S” mint mark and released in some proof sets. The mintage is estimated at the life of a proof die, which at the time was 3,000 to 3,500 coins.