ALSO keep in mind that we arent just talking the difference between a standard automag rail and an automag rt style rail.
The REAL RT is the very oldest style that is not compatible with ANYthing at all besides its own specific parts.. This is the trigger frame that has a larger rear hole to accept a different kinda screw.
The "rt rail" your talking about is really an RT pro rail which is from the later RT replacements. These guns were lighter and compatible with other automag parts..they basically dropped the original RT completely.
Although tom kaye did say that the original RT was built to some higher specifications and its maximum cycle speed or whatever is potentially higher..but it doesnt matter.
ReTro is a play on words like posted above..it came around when there was the old RT and the automag..and no automag compatible RT valve.. then the ReTro came out..then the rt pro basically using a retro valve and then everything else.