Board Thread:Questions and Answers/@comment-29781768-20171220214633/@comment-4436931-20180109121505

Just because Roswaal's gospel is more complete than the Witch Cult's own doesn't mean it's omnipotent, only Echidna has the book that reveals everything, and Roswaal's own can be lacking, like Subaru pointed out in Arc 4. Although he knew that Subaru was able to return back in time, he didn't know how he was doing it (the gospel didn't clearly state it), and whatever is written in the book can change, as shown when Subaru overturned the situation to win the bet against him