As of my last knowledge update in January 2022, there is no widely recognized instance of a 1975 No-S Roosevelt Dime. However, I can provide some general information about the No-S Mintmark varieties and their significance in numismatics.
In the context of Roosevelt Dimes, the absence of the mintmark (the "S" indicating the San Francisco Mint) when it should be present is considered a mint error and is highly unusual.
Minting Errors: Minting errors can occur during the coin production process, and one such error is the omission of the mintmark. This can happen if a working die fails to receive the mintmark impression or if the mintmark is inadvertently polished off the die.
Collector's Rarity: No-S Mintmark varieties are highly sought after by coin collectors due to their rarity and the unexpected nature of the error. Collectors often find these coins intriguing and valuable additions to their collections.
Verification and Authentication: Authenticating a No-S Mintmark variety is crucial, as counterfeiting attempts can occur. Numismatic experts and grading services can verify the authenticity of such coins.
Value: The value of a No-S Mintmark variety can vary based on factors such as the coin's condition, rarity, and demand among collectors. Coins in uncirculated or high-grade condition tend to command higher prices.
It's important to note that the information provided here is general, and specific details about a 1975 No-S Roosevelt Dime would need to be verified through reputable numismatic sources, auction records, or expert opinion.