The 1877-S Dime has a fairly healthy mintage of 2,340,000 pieces, but most collectors find this date to be elusive in high grade. This is an attribute that seems to be common to many of the S-Mint issues of this era, and it may have something to do with the distance of the San Francisco Mint from the collectors in the Eastern U.S. This date usually comes well-struck, but the mintmark often appears as a blob. The PCGS CoinFacts Condition Census begins at MS65 and ends with a single PCGS MS67 as the finest-known example).
Dime researcher, Gerry Fortin, has identified 14 different die varieties for this year, all of which have Type II reverses (the end of the ribbon on the left side of the bow ends in a single point). He alludes to the existence of a Type I reverse 1877-S Dime, though no actual example has ever been seen. Since the 1877 and 1877-CC Dimes are found with either a Type I or a Type II reverse, it is reasonable to assume that a Type I reverse 1877-S Dime exists.