It’s so bad that my fiancée has some bras that say she’s a B cup and others that says she’s a D cup. In order to go bra shopping, you have to actually try them on to find out if they fit.
If I had to try on underwear to see if they fit, I might not bother with underwear at all!
They still buckle a bit unfortunately, unless they’re a full-on sports bra that is squashing them as hard as possible and giving me the monoboob look. I’ve also found that a properly fitted bra that has the wire for structure actually makes me look slimmer overall, probably because my band size is actually on the narrower side. So I’ll occasionally wear the one non-wire bra I have when I don’t care as much about it looking good under my clothes. But even then, when it buckles on the side, the bra still kind of sticks out under my arms so it’s still uncomfortable.