Official Mint Sets are specially packaged by the government for sale to collectors. They contain uncirculated specimens of each year coins for every denomination issued from each mint. Unlike the Proof Sets, these are normal coins intended for circulation and are not minted with any special consideration for quality. Coins struck only as Proofs are not included. Uncirculated sets sold by the Treasury from 1947 through 1958 contain two examples of each regular issue coin. These were packaged in card-board holders that did not protect the coins from tarnish. Nicely preserved early sets generally command a 10 to 20 per cent premium above listed values. No official mint sets were produced in 1950, 1982, or 1983. Since 1959 sets have been sealed in a protective plastic envelope. In 1965, 1966 and 1967, Special Mint Sets of higher than normal quality were made as a substitute for Proof Sets which were not made during that period. Similar specimen sets dated 1964 are reported to exist. The 1966 and 1967 sets were packaged in hard plastic holders. Privately assembled mint sets, and souvenir sets produced for sale at the Philadelphia or Denver Mints, or for special occasions, are valued according to the individual pieces thay contain.