As time has passed, the market has matured for State quarter dollars, which were introduced by the U.S. Mint in 1999. Zeroing in on the underlying market changes for these quarter dollars simply comes down to grading and their totals by grade per issue. As time has passed, populations of third-party certified State quarter dollars have grown immensely.

Increasing market maturity has shown us which issues are scarcer than others in specific grades. In general, the high-grade Proof quarter dollars – the Proof 69 and Proof 70 grades – are much more common than the same grades in Mint State assigned to circulation-strike issues. The primary reason is that Proof coins are struck with greater care than circulation-strike quarter dollars and are issued by the Mint in protective holders. Circulation-quality coins are struck with less care and are released in bulk for circulation, and in Mint-sewn bags and rolls for sales to Mint customers. The way circulation-quality coins are handled after striking results in contact marks, also known as "bag marks," that lower their grades. Most ultra-high-grade circulation-quality State quarter dollars have come from the annual Uncirculated Mint sets.

When Coin World added valuations for these ultra-high-grade State quarter dollars in 2002, the graded populations were very low to nonexistent. Therefore, we stopped with Mint State 67 for circulation-strike State quarter dollars and Proof 69 for Proof strikes. Now, with much higher populations of graded and certified State quarter dollars in grades higher than those, we've added MS-68 through MS-70, as well as Proof 70. And because the Proof 70 grade is almost always graded "ultra cameo" or "deep cameo," we've opted to list only "PF-70DC," as the Coin Values listing abbreviates it.

As a general trend, values for most State quarter dollars have softened because their graded totals have risen dramatically in relation to demand. Registry collecting has helped support their values, though, as have all the new collectors coming into the coin market, purchasing certified coins rather than just collecting from pocket change. Data for the highest-grade Mint State values, though, has been difficult to find.

In addition to adding the ultra-high grades for these quarter dollars, we've added values for the 2004-D Wisconsin quarter dollar variants that were discovered late in 2004 with marks that resemble an extra leaf on the ear of corn. Two versions have been found, one with an "extra leaf high" and one with an "extra leaf low." The marks are the subject of an ongoing investigation by the Treasury inspector general's office intended to determine how they occurred.

Both variants are circulation-strike coins, produced at the Denver Mint only. Estimates by Bob Ford, the discoverer of these variants, and by Eagle Eye Rare Coins of Tucson, Ariz., put the populations between 3,000 and 3,500 of the Extra Leaf High coins, and between 4,500 and 5,000 of the Extra Leaf Low coins. Most of these coins were found in the Tucson area.

Also, because the 2005 Uncirculated Mint set coins have a Satin Finish, we've added valuation designations for those coins from the Lincoln cent denomination up through the Sacagawea dollar denomination.

Remember, too, that the values listed are just guides. Coins graded by varying services trade at varying prices.