In mid-1964 the Treasury Department announced that the Mint would not offer Proof sets or Mint sets the following year. This was prompted by a nationwide shortage of circulating coins, which was wrongly blamed on coin collectors.
In 1966 the San Francisco Assay Office began striking coins dated 1965, for inclusion in so-called United States Special Mint Sets. These were issued in pliofilm packaging similar to that of recent Proof sets. The coins in early 1965 Special Mint Sets are semi-brilliant or satiny (distinctive, but not equal in quality to Proofs); the coins in later 1965 sets feature very brilliant fields (but again not reaching Proof brilliance).
The San Francisco Assay Office started striking 1966-dated coins in August of that year, and its Special Mint Sets were packaged in rigid, sonically sealed plastic holders.
The coins were struck once on unpolished planchets, unlike Proof coins (which are struck twice on polished planchets). Also unlike Proofs, the SMS coins were allowed to come into contact with each other during production, which accounts for minor contact marks and abrasions. To achieve a brilliant finish, Mint technicians overpolished the coinage dies. The result was a tradeoff: most of the coins have prooflike brilliance, but many are missing polished-off design details, such as Frank Gasparro’s initials on the half dollar.
All 1967-dated coinage was struck in that calendar year. Nearly all SMS coins of 1967 have fully brilliant, prooflike finishes. This brilliance was achieved without overpolishing the dies, resulting in coins that approach the quality of true Proofs. Sales of the 1967 sets were lackluster, however. The popularity of coin collecting had dropped from its peak in 1964. Also, collectors did not anticipate much secondary-market profit from the sets, which had an issue price of $4.00, compared to $2.10 for a 1964 Proof set. As a result, fewer collectors bought multiples of the 1967 sets, and today they are worth more than those of 1966 and 1965.