Well, I did the bra tutorial thing, and I ordered myself a new bra at the size I am supposed to be to see if it fit. I was sceptical. Very much so.
I mean, all my bras are currently 36G and that is pretty damned big. Last time I was measured, they told me I needed a 40 DD which I knew was bullshit because they took my underbust measurement and ADDED two inches.
So, I did the thing, and measured it all and worked it out. I came out at a 36JJ
They don't even sell those in shops around here, so I couldn't go try one on. So I ordered it. It came today. I am never sending it back.
It's comfortable. It fits me. It's the right size. And my boobs look great! (Which they do anyway, but now they look even better!)
So there we have it. The tutorial works. I am a 36JJ in bras.