I don't think that's the case. I highly doubt that a 36AA is equivalent to a 32D. Also, Kim Kardashian is a self-proclaimed 32DD and my mom is a 36C and they look about the same size. It would be noticeable to me if there was a 2 cup size difference between my mom's breasts and Kim Kardashian's breasts. Kelly Brook is a 32E and her breasts are definitely bigger than my mom's.
You have to remember the difference between bust and under bust is relevant as well. Even though both a 32D and a 34B have a 36" bust the 32D has 2 extra inches of projection from her ribcage. I know you probably know this but the reason you go up a cup size when you go down a band size is because two pairs of breasts of the same size on two different size rib cages will project differently depending on which ribcage is wider. The confusing thing that bra manufacturer's don't tell us is how they know this difference in projection leads exactly to a cup size down for each band size up.
Also, keep in mind that bra sizes vary greatly even within the same brand. I have 2 VS bras of the same size (both are demi) and I fill one significantly better than the other. I also have one 34A that I bought at walmart that's huge on me and another one that I almost fill out. The shape also differs.
Edit: Also, perhaps if you reach 37.5" you will be busting out of your 34C.
You have to remember the difference between bust and under bust is relevant as well. Even though both a 32D and a 34B have a 36" bust the 32D has 2 extra inches of projection from her ribcage. I know you probably know this but the reason you go up a cup size when you go down a band size is because two pairs of breasts of the same size on two different size rib cages will project differently depending on which ribcage is wider. The confusing thing that bra manufacturer's don't tell us is how they know this difference in projection leads exactly to a cup size down for each band size up.
Also, keep in mind that bra sizes vary greatly even within the same brand. I have 2 VS bras of the same size (both are demi) and I fill one significantly better than the other. I also have one 34A that I bought at walmart that's huge on me and another one that I almost fill out. The shape also differs.
Edit: Also, perhaps if you reach 37.5" you will be busting out of your 34C.