Thanks guys, I'm glad you enjoy this as much as I do!
For the moment, I only focused on bellies because they are easier to separate in discrete categories. For breasts and butts, however, I could not figure out how to characterize them other than with subjective terms like "big" "medium" and small". It would be indeed interesting to use them to further classify the bodies, so if you have any idea, I would love to hear it.
Another interesting thing I noticed is that one body type can evolve into another one as the girl gains, usually starting with a (BCD) before rolls appear and sometimes get fused together when more weight is added.
@extra_m13 My favorite one is the (B/C)/D type, but everybody has its own preference and I hope that I can help people to word them better with this classification.
Beside genetics, maybe the way women wear their pants could have an impact? A fun experiment would be for someone thin to start gaining weight wearing a tight string around their stomach all the time to see if it makes them gain into a double belly or not.