I read these two posts by Rob Conley and Douglas Cole with interest:
OBS Content Program is terrible and it is now not just an opinion.
Not Opinion Anymore: Clarifications on the terms of DM’s Guild
So it seems like One Bookshelf's "DM's Guild" effectively works out to be work for hire - retroactive, if you've already done it.
Work for hire means what you produce belongs to the company, not you. That's how I work for SJG. It's fine, because my contract said that plainly and it's what I agreed to. A flat fee or a set percentage of the sales, but then the work belonged to them. If I reuse it on my next book, I technically need to account for that as it comes it out of the pay for the next book - they already paid for it. If someone else uses it, I get a piece or a paycheck.
But if you wrote with the expectation that you'd be producing a book and could re-use your own words and ideas later . . . it sounds like you are out of luck. And it took some clarifications to make that clear.