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!
When I was 25, my girlfriend complained about buying the same bra, same size, same material, same URL, from the same company, on their website, 2 years apart. The first ones fit really well, the second ones didn’t fit at all.
Meanwhile, there’s a shoe that I buy a pair of every few years. They release a new “version” about once per year, but the fit has been consistent, so I’m over a decade, and 6 pairs, into my purchase of them, with no problems.