In 1964, the government was struggling with a national coin shortage.  1964 was the last year of 90%
silver halves, quarters and dimes.  The Coinage Act of 1965 changed the metallic content of silver coins;
halves would be 40% silver clad, quarters and dimes would be entirely clad. The nationwide shortage
was due to rising silver prices and the vast hording of all coins including cents.   Eva Adams, who was the
director of the mint at the time, blamed coin collectors for the shortage.  Beginning in 1965, Eva Adams
eliminated mint marks from all U.S. coinage.  Furthermore, Ms. Adams ended the production and sale of
proof sets.  To meet collector demand, the mint issued special mint sets (abbreviated SMS) in 1965,
1966, and 1967.  The coins in these special mint sets were struck on specially polished dies.  These dies
did not produce coins that had the same quality of previous proofs, and were often only slightly better
quality than business strikes.  Some special mint coins have a cameo appearance and command a
higher premium in the market place.   Additionally, the quality of special mint set coins improved from
1965 to 1967.

There are also some examples of special mint sets from 1964.  It is unknown why the mint produced
these sets, but the consenting belief is that they were produced as trials or prototypes.   It is believed
that a majority of known sets today were part of Eva Adams estate, and were purchased by coin dealer
Lester Merkin.  Lester sold the sets at a Stack’s auction in the early 1990’s.  It is believed that there are
less than 50 sets in existence today.  PCGS has certified 22 Lincoln cents, 18 Jefferson nickels, 22
dimes and 28 Kennedy half dollars as 1964 SMS coins.   1964 SMS coins are considered extremely
rare.   The highest graded PCGS 1964 SMS Lincoln Cent is an MS68RD example.

In 1968 the mint resumed the production of proof sets, and the placement of mintmarks on U.S. coinage.  
Special Mint Set (SMS) Lincoln Cents
A 1967 SMS Lincoln Cent, Image by Jason Cuvelieir
A 1964 SMS Lincoln Cent, Image by Heritage Auction Galleries