Ironsoul, that was a good idea, but was there a follow-up thought that I'm not seeing? I think exporting as FBX does in fact produce normal UVs (I'm guessing from the texture maps that I had it save to the folder, I don't know how to determine this in a more technical way) but the M4 UVs still do not cover the entire figure, there are gaps where the geografts were.

Would welcome a plain language explanation of why. "Because a surface cannot utilize more than one UV map" comes off as a nonsequitur to me in that context, following only that they "divide the surfaces differently." My understanding of UV maps in general is that they are different ways of dividing the surfaces. Wouldn't each point on one map still correspond to a single point on the other map? Obviously the answer is "no," but why not?