That is not true. While PCGS does uses SP on SMS and Specimen coins, they don’t consider SMS coins as Specimen. The SP on SMS coins is for Special, as in Special Mint Set, not Specimen.
In fact they describe Specimen coins as such:
Specimen
Term used to indicate special coins struck at the Mint from 1792-1816 that display many characteristics of the later Proof coinage. Prior to 1817, the minting equipment and technology was limited, so these coins do not have the “watery” surfaces of later Proofs nor the evenness of strike of the close collar Proofs. PCGS designates these coins SP.
Nowhere in their description do they state SMS coins are Specimen strikes.
Special Mint Set
A set of special coins-neither business strikes nor Proofs-first struck in limited quantities in 1965 and officially released in 1966-1967- to replace Proof sets, which were discontinued as part of the U.S. Mint’s efforts to stop coin hoarding. The quality of many of the 1965 coins was not much better than that of business strikes-but by 1967, some Special Mint Set (SMS) coins resembled Proofs. In fact, the government admitted as much when it revealed how the 1967 issues were struck. In 1968, Proof coinage resume. There have been similar issues since; the 1994 and 1997 Matte-finish Jefferson nickels, for example, are frosted SMS-type coins. There also are a few known 1964 SMS coins, these likely struck as tests in late 1964 for the new 1965 SMS strikings.
Do you see Specimen Strike on any of the SMS coins?