No one but GM can post in Adult game public thread
My understanding is slightly different, Horus.
Public:
All Rpol members can read Public material, but additionally, the general public (non-members) searching a related topic via a search engine, can read it. This is also true of the forums. The messages in this thread, for example, could be found on Google by anyone, if they applied a specific enough search criterion, or if they accidentally stumbled across them.
Group 0:
Any member of Rpol can view Group 0 material if they log into the game, they don't need to RTJ and be accepted. Since unlocked Game Notices can be posted to by Players, I presume Notices are also Group 0.
Groups 1-Y:
These can only be read by players and lurkers who are assigned to those groups by the GM. Nobody outside of the game can read them.
Group Z is like 1-Y, but only the GM can post there. Anyone in Group Z is automatically not in 1-Y, making it potentially a Time Out zone, where players can listen but not respond.