Sheesh - I've been using RA-4 paper all over the place to print Color Negative images. You mean - the stuff was intended for reversal film??
Sarcastic key [off]. Seriously .. the "c" was derived from (C)ibachrome - which is a direct positive paper. The "R" as in "RA-4" paper is from -- I haven't a clue. Could it have something to do with "resin"??
I know it replaced the "old" EP-2 process ... I would imagine that was from something like "Eastman Process, edition #2..".