Well, that's the fun part......
On paper, say, a Sig P239 is about the cleanest example of what could be considered an LTC-B handgun. No large cap mags were ever made for it, at least not by the manufacturer. 10 is the top capacity, and only for the 9mm model.
On the other hand I can take 2 of these 10s, cut and weld them together, and (probably) make a 20 round mag that will function in the handgun- Now is the P239 "capable of accepting"? Of course it was, it always was, just like ANY other firearm that accepts a magazine.
If one takes that statement literally, it basically means that LTC-B holders can really only lawfully possess three types of handguns:
-Revolvers;
-Weird semiautomatic handguns like the (Grendel?) pistol which have an internal, non removable magazine of 10 rounds or less.
-Derringers and other single/double/triple/quad shot handguns.
I think the reality on the ground is that is clearly NOT the case. GCAB/EOPS/MA doesn't take that wording literally, otherwise LTC-B holders wouldn't be able to buy things like single stack semiautomatic handguns in most gun stores in MA.
-Mike