Men of Lemmy, how old were you when you found out that bra cup sizes are not standardized in the slightest?
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!
That inconsistency is not exclusive to women's undergarments... I bought a half-dozen of the same American Apparel hoodie in different colors... very different fits.