You're probably right. SMS sets were only issued by the Mint in 1965, 1966 and 1967. In 1964 Proof sets were still being issued so an SMS wouldn't have been produced. However, something was issued in 1964 which wasn't a business strike and wasn't a Proof. According to the Red Book:
1964 Special Strikes
In addition to the normal SMS coins dated 1965–1967, there are other, very similar pieces dated 1964. These coins are unlike ordinary Uncirculated and Proof coins made that year and have characteristics akin to the SMS pieces. Collectors generally refer to the 1964 pieces as Special Strikes. All denominations are very rare, whether sold as single pieces or in sets. It is unknown why these pieces are rare (whether sold as single pieces or in sets), why they were made, or how they left the Mint.
According to The Red Book (2022 Edition) the 1964 Special Strike coins, Cent through half dollar is valued at $15,000–$20,000 compared to about $10 for the 1965, 1966 and 1967 SMS's.
NGC puts the value of the cent coin (SPRD 67) at $9,500.