Chris,
Every mfr was REQUIRED to supply S/Ns for pre-ban SAW to BATFE and that is the baseline that BATFE used to determine if it was exempt or not.
Still should hold with MA law, but one never knows with the morons on Bacon Hill.
Also realize that a lot of what you could do was in CFRs (Regs to interpret the law) and those did NOT translate over to MGLs and EOPS is/was of no mind to create CMRs to clarify any of this stuff (i.e. mirror the Fed CFRs)!
So it could be a long road and expensive one thru the court system trying to convince an anti-gun judge/jury that we should be able to do in MA what the Feds let folks do during the AWB (with no MA legal precedent to back you up)!