I imagine that in this case there isn't an official NDA aggreement, but something more verbal and based on trust - and the knowledge that if these individual violated that trust that Tor would cut them off, which the leaders of these places wouldn't want.

I have exchanged a few emails with Dot, and she said that the copies didn't come from her (and she's Sanderson's publicist). So they obviously came from someone else (heck, possibly even the top dog himself, Doherty, particulary in the case of Jason over at DM or just as likely, through Harriet).