I bought these to have comfortable at home bras. I oscillate between a 36 and 38DD, depending on the brand. I sized up here, merely b/c the last bras I bought were the bigger size, I thought maybe I'd just gotten bigger. The black bra fits well. The white bra, totally different cup size. I laid one on top of the other and it's obvious the white cups are a lot bigger. When I put that one on, fabric gaps, I have to use the third hook in the back, etc.

So, not sure which of these bras is actually the 38DD, but they are definitely two distinctly different sizes. Be aware that it may happen to you as well.