They re-used the name. How confusing. This is the set I have:

http://poserworld.com/Downloads/Other.Figures/9398/Mia.set.aspx

I don't have the V4 Mia Dress, sorry.

Anyway... Do you have UVMapper Pro? If so, open the geometry file in there, and do Select > Facets > N-sided, then choose 'More than' and 4 sides. That will tell you if there are any >4-sided polys, which is what I would have looked for had I owned the clothing in question... (deep breath)

For dynamic simulation, triangular mesh is best; UVMP can do that for you too, along with any welding that may be needed.

I'm a bit surprised that the dress isn't set up for dynamic (or at least hybrid) use, since Steve generally makes dresses and skirts that way nowadays. Just seen aRtBee's post, I see we are of the same mind. :)