Bras from Poland are awesome, just saying.
I'm a 32JJ/J, I can fit into a J if need be and some J's fit better than JJ's. My fitters at my specialty shop tried to put me into a 30K cup...I couldn't beathe so instead of figuring that I needed a larger band, they put an extender on the bra and told me it'd fit better once I got used to it (I've been wearing the correct size bra since I was 18...I'm 25 now). Many fitters are determined that they are correct and that their method is the ONLY method that works. It also doesn't help that most of the UK bras are meant for women who have wide roots and are a full on bottom shape. I used to try on between 5 and 12 bras in my size from my specialty shop before finding 1 that fit sort of correctly. If I didn't struggle for years finding the correct size, I'd be wearing a bra that was uncomfortable today. It also doesn't help that the bras are so expensive. My Polish bras are cheaper to buy from Poland and get shipped to the US than to buy a UK bra from the US.
Fun fact about bra manufacturer's: Bra manufacturer's construct bras based on the population of that country's breast shape/root is. So in the UK, most women have wide roots so the manufacturer's make bras to fit this shape...in Poland, most women have narrow roots and so the manufacturer's make bras to fit that shape (you get a more projected look when you have narrow roots). Curvy Kate, though, seems to be trying different things...some models work best of those who are full on bottom and NOT heavy with wide roots and others work well on women who have narrow roots and are more full on top. I think they're either trying to see what sells the most or making both in order to maximize profits from both sides of the table.
Anyway, when fitters either don't know or don't understand how breast shape and root take part in the sizing process, you have women who end up in the wrong size-besides the typical add 4-5 (I've even seen 6) inches method. That and the availability of sizes. The US right now is very slow to recognize that most women wear between a 28 and 32 band and most women don't think they could wear below a 32 band size because the band feels too tight-even though this is caused by a cup that's too small and the band being pulled too far forward to cover breast tissue. These two combinations are what causes probably 70% or more of women wearing the wrong size bra. Misinformation and availability with probably a little bit of stigma (although the amount of women who want bigger breasts seems to be huge!) about large breast. I do believe that's why brabandproject.com was started though.
I'm currently getting a grad degree in marketing and I really wanted to study bra sizing and advertising/promotion for my thesis but my advisor is a man and I didn't feel comfortable discussing the extremes of the topic with a guy but oh what amazing joy it would be to find out! I may still do a study since I want to open a bra shop one day.