It is my understanding that pre-ban dated or unmarked will suffice. I think I would prefer dated just to be sure.
Yes, MA. retained the assault weapons ban. Thus it must meet the standards of a rifle under MA. Law. Please, I do not wish to turn this into a post about how crappy MA. is. We know, agree and do what we can while we can. Funny that the area know for the birth of the county (with a gun by the way) is quickly working to eliminate the second amendment.
Thanks for everyone's help and sympathy thus far. I have sourced some pre-ban 20 round mags thus far. Still I would like to have a few 30 round mags. With the cost of ammo these days I do not picture even taking out 20 round mags and blasting away. I will probably also get some 10 round mags for regular use. I just know that it is not going to get easier to get magazines in this state and if I stock up now I do not have to worry later.