Ron Guth:
The 1871-S Dime has a small mintage of 320,000 coins, but this is in line with many of the preceding years, Nonetheless, this date is more valuable than P-Mint dates with even lower mintages (1869 comes to mind), mostly because of the attrition of Mint State examples as they travelled across the country from the San Francisco Mint to the collectors back east. Perhaps two dozen Mint State examples are known, mostly in MS63 and MS64. Gems are very, very rare, and none are known above MS66.
Dime researcher, Gerry Fortin, has identified three different die pairs that were used to strike all of the 1871-S Dimes. All three varieties have a small, weak mintmark.