User blog comment:B214/High School DxD EX/@comment-26890593-20150821161049/@comment-24502975-20150821205819

"along with the entire anime series"

Doubt it. BorN is an AU but the rest of the anime is just an adaptation rather than a separate world connected to the LN.

"some guess they travel back in time right after Vol. 21, or to an earlier Volume"

You mean the timeframe they arrive at? Yeah, I'd love to see Ishibumi hint at that later on in EX or a future volume.