2018.5 revisited. Just noticed that, at least, plural RGs is another basic one not yet auto-magified (today’s source), so:
RGs = Release Groups
I do not know about Rs and have no time to counter the forum feature ([Ctrl + F] hijacked to tunnel vision (i.e. not searching a fully expanded thread) and search excluding both ‘Rs’ and ‘ Rs ’ as too short), but should it not be routine by now for this thread, if someone proposes XYZ, to anticipate and admin the plural XYZs also; and do a retroactive sweep of this thread while it is just some 100 posts?