All these lenses (1cam, 2cam, 3cam, R-only) are R-lenses but how many cams does your lens have. If you can change the aperture without noticeable change in the metering values then probably your lens is not for R cameras but for Leicaflexes, it can be mounted and work on your camera but won't fully cooperate with the camera's light meter. It would be easier if you could show as an image of the mount of your lens.
Stop down metering (in a word) is metering with aperture closed to the set value but I am sure that this has been discussed in an earlier conversation, please do a little search.