User blog comment:Xilinoc/Zanpakutō & Tōjū arcs - Review/@comment-4484409-20140124182900/@comment-5398287-20140125003801

Well, Kubo has some level of involvement in all of the filler arcs, but his additions and creative directing don't necessarily make it canon. However, I feel that the appearance of each Zanpakuto spirit correlates very well to however much we know about them.