I think it was gradual changes over time. The V2's that were manufactured closer to the release date of the V3's probably have all the guts, minus the magnetic grills. I don't think your going to find a schedule or anything that will tell you. Just call Axiom and give them the serial#, they can tell you, or email Noreen.

M80s VP180 4xM22ow 4xM3ic EP600 2xEP350
AnthemAVM60 Outlaw7700 EmoA500 Epson5040UB SonyUBPX800