Transferring weight maps will show it, like WandW said.

It will also show duplicate vertices depending on the value mapped to them.

You can take a character into a modeling program (Blender,etc) and check to see if the edge loops are correct and look for other issues.

Openings in the wire frame must be one loop, and a lot of times they are not. (eye sockets, fingernail areas, teeth, etc.)

Errors like this might not affect weight mapping because of where they are. When those areas are mapped, they are usually mapped to 1. (1=full joint effect)

There are areas in V4 mesh that have improper edge loops, but the are not in areas that present a problem with the weight mapping because they either are not mapped, or a value of 1 is applied to them.

 

I checked J6, there are more than a few symmetry errors as well.

The back of the chest has a symmetry and a grouping error at the center bottom at abdomen.

That one error instantly affects two body parts, breaking symmetry on both body parts.

Simple errors like that are no big deal with standard rigging, but present problems when weight mapping. It might not sound like much to have the chest asymmetrical, but there are a lot of maps on the chest, and most of them would not be symmetrical due to the error in the mesh.

There would be 50 plus maps, just on the chest.....

And it just compounds from there since the abdomen is not symmetrical either.....

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