To be fair, Kubo retconned that entire thing. When Kenpachi was first introduced, he called himself Kenpachi from the beginning (before joining the court guard squads) because he was the greatest swordsman, and he named himself Zaraki because he was from the Zaraki district.
Kubo's just an idiot who forgets his own lore sometimes.
Also, information on the next Bleach movie (picslol) being released a year from now:
Spoiler: show
XI Wiki


