If the magazine is identical to an M1a magazine, pretty sure that it will need to be marked at manufacture as MVP specific.
Otherwise it will be considered the same as a pre-existing product i.e the M1a magazine; therefore it has to be pinned. There is precedent for this. This is why CarverKs AK mag needs to be pinned, but Beowulf mags do not, and why AIA mags are good to go in M305s.
From the fact that a range of magazines fit - i saw a video where a Magpul P-Mag fit, in addition to DPMS mags and M1a mags- i don't think the MVP mag can be identical to an M14 mag, or we'd be able to fit P-Mags in our M305s, which as far as i know, we can't.
Just some reasoning - no hard evidence to back this up - but i can say that spotting that MVP video this morning while walking the dog has certainly cheered me up.