A couple of things tend to confuse the issue. First, Massachusetts law doesn't care about C&R FFLs or even 01 (dealer) FFLs. Whenever Mass law refers to a licensed dealer, they mean a holder of a state license to sell firearms, not an FFL. The other thing that makes confuses things is the tendency to talk about things that Massachusetts or federal law allow. Laws don't allow anything; they prohibit or restrict certain things. Massachusetts law prohibits sale by an individual resident to another individual resident unless both are licensed properly and the seller has made no more than 3 previous private sales during the year. It says nothing about private sales to a resident of another state. Federal law, however, requires that all sales between residents of different states go through a federal licensee, i.e., an FFL.
Ken