I can only understand your plight.
We have to look at this as a phenomenon.
Simply put, bra sizes are just confusing! Period!
If I were in your shoes, and female, I would have been dumbfounded.
I'll list a number of reasons:
What size? 30A, 52B, 70D, 40E? And don't forget we could have various combinations like 30AAA, 52BBB, 70DDD, or even 40EEE. That's not all, the puzzle gets confounding with quarter, or half sizings.
Asian size? Which brassiere companies create bras specially for female Asians? Perhaps a girl's closest match is to get a set of bra from BeeDees, in the kids' section.
Cold weather/Warm weather? Physics 101, heat expands, cold contracts, 'nuff said.
Last but not least, I could list a number of other reasons, but I'll leave some room for discussion.