Board Thread:False Info and Speculative Discussion/@comment-4091815-20160202180218/@comment-26879545-20160202220631

HolyDrumstick wrote: AND, it still doesn't make it ok that he listed banshees as non-supernatural before is was actually canon. Just like Nervous told you before, it was literally canon before this e-mail... They didn't make it very clear, no, but it was and still is canon. The only difference is that now, we have the Word of God making it clear.

However, it's also like Paul says. They can change this at any point before the show is finished. If another writer wants to say Banshees are supernatural and exceptions to the "Mountain Ash" rule, then that will be the new canon should it be stated on screen.