They really are exaggerating cup-sizes. 
Piss off are main girl's boobs K-cups. They haven't got any bigger from when they were claimed to be I-cup or even G-cup.  They're barely different in most shots from that other girl who was actually listed as G-cup, and at least on page 12 they're CONSIDERABLY smaller. 
As for that loli, she isn't above an A-cup, but they gave her a token B for nothing.  B is small, A is nipples on a washboard, and she has nothing there...  or at least not when they actually say it. There is something there on page 28.  Can chalk that down to artist inconsistency.