I might be wrong on this, but I don't think you'd see doubling on the mintmark on a DDO from that time.
Generally speaking, you're right; it's often a good indicator. However, it is not an absolute, and a coin certainly can display both a doubled die and an RPM. In addition, a post 1989 cent can display doubling on both.
My pick up point was mostly the top left of the 9 as seen in Wexler and Variety Vista, neither show an rpm south, I included it because it was there. The rest of the coin is too worn to show any other points.
