User blog comment:B214/High School DxD EX/@comment-3965848-20150727054413/@comment-26209278-20150727113018

If they restored the LN timeline into the anime for season 4 (ie, using volume 8-10), without referencing this story, it might confuse the anime-only fans who wouldn't know that this happened.... So i feel like it kinda needs to be animated before they carry on with the LN.