@ ghelmer -  I think you're right. (I ashamed to admit that) I was watching Oprah the other day and the topic was "the proper way to fit a bra". Indeed the numeric measurement is the rib cage underneath the breasts. So women that thought they were 36 D turned out to be like 32 GG (I guess it's common now for stores to carry up to double J).

I have no idea how any of this relates to V4.