By the mid 20th century, with the growing market for rare coins, the American Numismatic Association helps identify most coins in North America, numbering coins from 1 (poor) to 70 (mint state), and setting aside a separate category for proof coinage.
In the mid 20th century, as the market for rare coins expanded, the American Numismatic Association began identifying most coins in North America, assigning them a numerical grade from 1 (poor) to 70 (mint state), and creating a separate category for proof coinage.