I'm not sure how he could have a data pad from Jango in a book, as it would contradict everything we believed until GL destroyed what was held as fact. Before Episode II we all thought that Fett started out as a Stromtrooper, killed his officer, became an outlaw, killed a Mandelorian, took his armor, and had Kuat specially build the Slave I. I guess it could have been in one of the Ep II books, but I haven't read any of those.