Bras are made out of stretch material, but a tape measure is not stretchy, so a 32 band should go around if you measure 32 around...
Unlike most clothes bras are now made so that the stretched out bra should measure what it says. If you have a waist that measures 29 inches would you buy 34 inch waist jeans? Equally would you expect every pair of 30 inch jeans to fit perfectly?
I can try on 10 pairs of jeans in the same shop, same size, some allegedly the same style but in different colours and not all will fit, same goes for bras! Balcony, Full Cup, Plunge is similar to bootcut, straight, boyfriend or skinny - some will work, some won't.
Wires are definitely different shapes, Curvy Kate are generally wide but a bit inconsistent in back/cup size. Elomi are about the narrowest UK sold brand (but start at a 32). Boux avenue notoriously come up tight in the band.
Random patterns I've seen - smaller back bras are much less stretchy as there's less material to stretch.
And for sports bras all the rules are different - basically if its comfortable and you don't bounce too much when you jump all is good, unless you're planning to wear it all day!