When the U.S. Mint introduced special commemorative coins in the early 1980s, they were sold individually and as part of Prestige Proof Sets. Most collectors bought their commemorative proofs individually, and most proof set buyers continued to acquire regular sets each year. The result is that Prestige Proof Sets have become BY FAR the scarcest form of these coins. The 256,954 mintage for the 1991 Prestige proof set was less than 10% of the year's regular proof set. That year's Prestige proof set contains the five regular annual issues as well as the commemorative Mount Rushmore silver dollar and half dollar in finest-quality proof form.