The game explores the world that Jim has constructed but it doesn't add to it.
Yes... but. From what I've read about the upcoming supplement it will include Jim-based information that hasn't made it into the series and may not, such as the fact that the Ways leading to the Gatekeeper's sanctum require a quick jaunt across the moon. We might get more substantive information that Jim has dropped on Fred but won't be working into the books.
On the specific question of the Accords, I don't know if a full copy of the Accords even exists, and if it does I doubt we'll see it before the end of the series, if then.
Or the one after that...
From what I've read Evil Hat doesn't have plans for periodic splat books, though personally I'd love it if they did.