Interesting thread-necro. I put the O in (O)D&D in parenthesis since it wasn't in the original name, then call the Advanced versions 1E AD&D and 2E AD&D. I sometime refer to the other branch collectively as Basic D&D though the differences and level-considerations often enough require mentioning them by writer/editor name. I often see the acronym D&D BECMI meant to cover the "red box" tiered system of Mentzer's Basic collectively. I collectively refer to WotC's previous edition as 3.XE though sometimes break that out as 3.0E and 3.5E. Everything since is 4E to me, though I have seen some refer to Essentials as 4EE or 4.5E, but the latter doesn't seem preceisely the case to me.