What's The Difference With These Kennedy Halves ?

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With the exception of 1965 through 1967, proofs have been struck each year in the same metallic composition as regular issue pieces. The first Kennedy half dollar proofs were struck in early January 1964. Early strikes depicted Kennedy with heavily accented hair; an estimated 100,000 coins were struck with this feature. This was altered for the remainder of the mintage of nearly four million proof coins. Due to the coin shortage, the Treasury Department announced that no proof sets would be struck in 1965. Instead, Special Mint Sets would be struck to satisfy collector demand. Coins for these sets, minted at the San Francisco Assay Office, were struck with no mint marks early in 1966 with heavily polished dies dated 1965. Similar sets bearing the dates 1966 and 1967 were also struck. A few of the 1966 halves from the Special Mint Sets are known with Gasparro's initials "FG" missing from the reverse, apparently because of an overpolished die. The first year's production was sold in soft plastic packaging; the 1966 and 1967 issues were sonically sealed in hard plastic cases. In 1968, regular proof coinage was resumed, although production of proof coins was shifted to San Francisco and the "S" mintmark added.