The US Mint makes commemorative coins annually. These coins are often well advertised and active collectors would recognize most of them if they saw them at a coin shop. But there are entire series of commemorative coins that most collectors will never see unless they actively seek them out.
The US started producing platinum bullion coins in 1997. For the uncirculated version of the coins the design has been the same. But starting in 1998 the proof versions have had a different reverse every year. From 1998 to 2002 they produces the ”Vistas of Liberty” series which had images of New England, the Southeastern Wetlands, America’s Heartland, the Southwest Desert and the Pacific Northwest. In 2003, 2004, and 2005 they had individual allegorical images. 2006-08 saw the creation of the “Foundations in Democracy” series which featured a coin for each of the branches of government. Since 2009 they have been producing a series called “Preamble to the Constitution”.
Collecting these coins is very challenging. Not just because platinum is a more expensive metal, but because the mintages are very low. Most of the one ounce proofs have mintages below 10,000 pieces. The last three years of platinum issues have a mintage of less than 20,000 combined!
There are many nuances to collecting platinum commemorative bullion coins, including: Uncirculated, Proofs, Burnished Uncirculated coins, and a Reverse Proof. There are also fractional issues (1/2 oz, 1/4 oz, 1/10 oz), however, the fractional coins have not been produced since 2008. So, even though the fractional issues have higher mintages, they are also hard to locate because the lower price points opens the collector market to more people. Platinum is currently below $1,000 per ounce, but most one ounce pieces trade in the $1,200-$1,800 range. The least expensive coins are the 1/10 oz pieces which trade anywhere from $110 on up.