Those type of item stats generally come from Japanese sites. Right after a food item is introduced, it's up to anyone to try to figure out what the exact stats are on it. Over time, the patch guides are published in Japan, and some websites double-check the known stats vs the official version (there are errors in those guides of course, but it gives a general idea of what the official stats are expected to be.) At somepage, we've used a bunch of different Japanese websites to try to dig up accurate food stats; one of my current favorites is GoblinClub FFXI.Originally Posted by Enkidu
As far as caps on Accuracy from sushi, there are some listed on food such as Tentacle Sushi. It's possible that the others have caps as well, although since Tentacle Sushi was added later, it could have been some attempt to give up accuracy at the expense of Double Attack, given the listed stats. It's been a number of months since I tried to verify all the food stats, so there could be more data out there by now, as well. Just glancing over the list on GoblinClub again, I see some more that look to be slightly different; something else to do.
XI Wiki

