Board Thread:General Discussion/@comment-27140233-20151102134649/@comment-8986886-20151102173004

Well, even if Kubo had planned to use something like the Valley of Screams later in the manga and had approved the use of it in Memories of Nobody, it doesn't automatically make the whole movie canon material. It would be similar to how the spirit of Katen Kyokotsu was first seen in the Zanpakutō Rebellion arc, before she was introduced in the manga. Perhaps you could also find similar examples from other arcs/movies if you looked hard enough, but I still wouldn't consider them to be canon as a whole.