User blog comment:Njalm2/Fanon Canon - Grimmjow's Espada!/@comment-2089817-20150116144217/@comment-3403804-20150116145940

I agree, it doesn't even have to be 13, it could easily be 20 as well, it all depends upon how many powerful individuals he could gather. The Shinigami have Lieutenants as well after all, and a whole army besides, not to mention the Royal Guard.