Wasn't it because there were different art directors in XII and XIII? Nona was the art director for XII and the one for XIII was Ritsu Yamaguchi?
(well according to this post here)
If you were referring to the "KOF XII/XIII male characters and female characters style" comment I made in my previous post, I didn't mean a difference between KOF XII and KOF XIII styles. KOF XII and XIII sprite style is the same (hence I wrote "KOF XII/XIII"), I meant a difference in style between male characters and female characters. Male characters usually look all right (except Clark and Ralf, in my opinion), while many female characters look not harmonious, with big bubbly heads, scrawny arms ("scrawny" comparatively to the rest of their body and general style of the game), too big eyes, etc.
I hope it's clear now =).