According to PCGS’ Jaime Hernandez, “From 1956 to 1964, the Philadelphia Mint inadvertently struck some circulation strike Washington quarters with a reverse design intended for proofs only. All regular circulation strike Washington Quarters from 1956 to 1964 will have a reverse design displaying the letters ES of STATES very close to each other and almost touching. A proof Washington quarter design is different, since it will display the letters ES of STATES separated from one another. Consequently, any circulation strike Washington quarter from 1956 to 1964 which displays a proof design is referred to as a Type B Washington quarter.”