The U.S. Mint did not issue regular proof sets from 1965 to 1967. Instead, high-quality "Special Mint Sets" (SMS) were substituted containing specimen coins that were of a higher caliber than those struck for circulation, but were not quite proof quality. Struck with 40% silver content, these SMS Kennedy half dollars are tough to find individually as they must be liberated from those hybrid sets. Our choice of 1965, 1966 or 1967 date.