You cannot actually unwrap the model in one frame while that unwrapped parts of the mesh are still connected in the other frames.

Unwrapping the mesh is only possible on the skin, because it doesn't touch the model in its shape in 3D.
The mesh on the skin picture saves only the information which pixels are in a certain polygon.

The (3D)frames are all identical in respect of their vertices('points') and polygons(faces) and connections.

That's what I just think relating on expieriences with the MED, I didn't really read it anywhere.
If I'm wrong, pleeease, correct me!