As previously referenced, there are two steps to MA approval. The first is to get on the appropriate EOPS Approved Firearm Roster as legislated in MGL c.140 s. 123 and s.131, and further regulated by EOPS in 501 CMR 7.00. The second step is for the manufacturer to certify compliance in writing pursuant to the AG's 940 CMR 16.00. The AG does not publish a list or roster.
Violations of the MGL are usually criminal, while violations of the CMR are civil. Both are intended to regulate the sale of "firearms" at the Dealer level. It's not illegal to possess firearms that are not on the Roster provided their design does not violate other MA laws (i.e. non pre-ban large capacity magazine). LEO's can purchase firearms that are not 940 CMR 16.00 compliant, but they must be on the Approved Firearms Roster. Receivers (frames) are legally exempt since they are technically not "firearms" under the MGL, although an ATF 4473 and approval are required.
Theoretically, the broad discretion granted to issuing authorities under the MGL could be the basis for revokation of an LTC held by an individual who is in possession of non-compliant firearms.
"We must reject the idea that every time a law's broken, society is guilty rather than the lawbreaker. It is time to restore the American precept that each individual is accountable for his actions." ~ Ronald Reagan