American numismatists have been blessed with extensive record keeping by the United States Mint. We know almost exactly how many coins were struck for any particular issue, even as specific as to the month, or even the day. This is unlike many other countries where such records were never kept or lost, making rarity determination much more difficult. Due in large part to these extensive records, we are able to determine the rarity and some of its causes for a number of intriguing issues, such as the 1878-S Seated Liberty Half Dollar.
The half dollar was one of the most popular denominations for much of the 19th century, struck virtually continuously at various mints in large quantities. The San Francisco Mint had struck approximately 5.3 million half dollars in 1877, yet the following year saw the creation of a rarity. The unique story behind the coin can be uncovered by examining the records available from the Mint and in particular the surge in production for the silver dollar.
Silver dollars had last been struck for circulation in 1873, when they had been replaced with the Trade Dollar, solely meant for use in overseas export. The whole situation would change again with the Bland-Allison act of 1878, which required the United States Mint to purchase a certain amount of silver each month and mint it into silver dollars.
The act had been passed after extensive pressure from Nevada, where the mines of the Comstock Lode were still turning out a huge supply of silver. When the Bland-Allison Act of 1878 passed it meant that all mints (Philadelphia, San Francisco, New Orleans and Carson City) had to turn out huge amounts of silver dollar each month. The massive increase in silver dollar production had a significant impact on the production of other silver denominations which saw their mintages drop dramatically for the next decade.