That in it yeah, the the prologue book is in the form of like a guide book but with lesser pages. Its goes on about the characters etc..the two novella's and prologue stats and such to the characters prior to Advent Children, ive not read the actual book, though i have read the two novella's. "On A Way To A Smile" & "Case Of Tifa"
EDIT: I think the voice they wanted to do Nanaki's voice is some big star in Japan and cameos as Nanaki, but normally big stars as cameos dont normally get loads of dialog. Maybe he could of had a few more lines, but i'd rather the perfect voice and a 1 liner than a crap voice and loads of dialog.