Just so you know, most suppliers of hi-caps simply won't sell to MA, period. Their shipping stuff will have a caveat about that.
Also, keep in mind that the burden of proof is on you that they're preban and you already had them. What will you do if MA authorities say "You're lying, you just got those and they're new."
How will you prove otherwise?
If MA has a law allowing only pre-ban magazines, I wonder how anyone could tell them apart.
Can't, and AFAIK, the burden of proof is on you. If MA decides to make an example of you and say you're lying about them and they're actually new...what're you gonna do?