ok so Robin's breasts were 99 an I cup and after timeskip a 100 J cup according to Oda
Nami's were 95 an I cup and after timeskip 98 a J cup according to oda
How can Nami's 98 be J's and Robin's 99 be I's?
I found these here http://onepiece.wikia.com/wiki/Nico_Robin
and here http://onepiece.wikia.com/wiki/Nami at the bottom of the page.