Female jellies: do you wear a bra size that was properly measured? (Potentially NSFW)

I have read that as many as 80% of women are wearing the wrong sized bra. I more or less know that I’m one of them, although I don’t have any of the telltale signs of a poorly fitting bra (sliding, falling, gapping, spilling out..etc). Today I decided that I would actually measure myself, and although I have my band size right, apparently my cup size is way off. I have heard that it is bad for your breast health to wear a bra that is too tight, so I thought I should look into at least trying a larger cup.
With this new (and daunting) information, I decided to look up multiple well known stores and websites that sell women’s bras, to find that none of them even come close to selling a cup size that would supposedly fit me…. and though I am busty, I am by no means in some extreme category. That leads me to wonder how in the world anyone could be wearing the proper bra size, unless all women with relatively large breasts are having their bras custom made.

Anyone with me on this? Have you ever found out your “official” bra size? Was it surprising? Do you buy bras in that size?