Potential prequel books

[Armitage]

No he didn't, actually. He said that you didn't need to have read the extra books to understand what is going on in the main comic, that he'd cover it in comic if it was necessary. He never said that that meant he'd keep out anything from the prequels.

Which is basically what I wrote in the last sentence you quoted, right?
Essential stuff will be in the main comic, so that people who haven't read the prequels can understand what's going on.

The first part of what I tried to say may be somewhat unclear.
What I meant so say is that he doesn't need to put everything that the Order of the Scribble knows in the hypothetical prequel book. He could just put stuff in there that doesn't spoil the main comic, so that he can reveal these things when the time is right.