Rear speakers were always an option. You could get any of the radio options with or without rear speakers.
I believe R22 is a "stereo" option. If it has a balance dial, it must be stereo. If it was one of the stereo options then it came with 3 in the dash and optional 2 rear. If it was a mono, then it came with 1 in the dash and an optional 1 in the package tray (on the drivers side).
If you have the rear speaker knob, you can tell the difference between the stereo and mono knobs. Also if you have a cross over box, then it was a stereo config.