Quote Originally Posted by Yukimura
They said when an Espada gets demoted they added two digits to their number. I would think they just tack 10 in front of whatever that espada's number was before he got demoted. Hence #103 would be former Espada #3.
Maybe he was number 10 and they just added a "3" to make him a 3-digit. But i wouldn't take the number system too seriously, because it doesn't seem to make much sense overall.