U.S. 1958 “Vintage” Silver 5-Coin Proof Set. Just 875,652 were produced over 50 years ago in the year that Alaska and Hawaii became states. No regular U.S. proof set since can boast a smaller mintage. And actually, substantially fewer intact sets exist today, because a good number were broken up to obtain individual Franklin silver half dollars, which were issued only as part of the 5-coin proof set.
U.S. 1963 “Last Franklin” Silver 5-Coin Proof Set. When this set was issued no one anticipated it would be the last with a Franklin silver half dollar. That series was scheduled to continue through 1972. But after the 1963 assassination of President Kennedy, it was supplanted by the new JFK type. The only way to obtain a 1963 proof Franklin half is to break up these proof sets, so fewer remain intact today.