[Katana]

There is no having bra sizes figured. Honestly. There've been women who have literally measured the bands on their bras and found that they can have bras labelled ANYTHING, and they'll actually all have the same band width. Or you can have any two bras with the same band size on the label, and they'll be RADICALLY different. Every time you go to purchase a new bra, it's like starting the adventure all over.

I hear you there.
Normally within one line/collection the size will be the same as others in the same collection. However if you go to a different brand, even in the same shop they'll be different. It's to make sure you keep buying the same brand, the one you know fits you properly.
That's why I never order bras online and always try every bra on first, even if they are all from the same shop.
I once had a 36F that had a band about 4 inches smaller than another 36F from the same shop. Ever since then I try on every bra I can find that seems like it might fit