I would see this as being a mod / co-mod responsibility to some extent. If a player asks you / tells you the context to something is not clear I can see a mod in all fairness either posting links to sources or encouraging the player to ask in game for same. Fundamentally whoever said something obscure is either lying and knows they can be caught by research, or is telling the truth and may just not have the time themselves to prove it.
The risk in a mod doing it is they may share info about the game inadvertently, or a player may get caught in wondering if the mod, omniscient as they are, is implying something about the current game.
Plus there are some mods who just want to mod, and don't really want to babysit and/or mentor. Or just imagine the variance based on who they got...
I will say though, that the downside with open games is they can be less engaging and become more mechanically locked. One aspect that the non trad mods may forget is that although you don't have time limits for the phases, maybe you should, because in person the social pressure to move on is huge. But in writing... pfff...
That's part of the draw of semi-open. But yeah, that's the problem with outlandish claims. It's pretty much always true that, no matter what crazy frakked up smurf someone claims, an actual game here has at some point featured something weirder and it seems we're all just out to out-weird each other.
How does semi-open set-up work? You give a list of possible power roles but don't say which are included?
That's one way - matrices are another option that's a little more precise. That's what a lot of MU games run off, and I used a modified version of this matrix: https://wiki.mafiascum.net/index.php?title=Matrix6
in the smurf game. But yes, you could also just list 10 possible roles (VT, mafia goon, Town Cop, yada yada) and announce at the start that some/all of those, and only those, are present in the setup.