Thanks for catching that Inbox bit. I'll revisit.
I think I see what you mean about document visibility not being relevant to external groups, because any content they know about is in a membership-controlled group and is not private, but isn't it technically accurate? There is potentially community content they can't see because the owners don't want them to, so if someone mentions Document X and an external user doesn't know anything about that document, this is a potential reason it is invisible.
Maybe I'm not understanding your point.
Hiya - underwater on a launch of a major external group hence my laser focus. Let me loopback ASAP.