Most decades old Selenium meters are seldom working today, much less accurate. Earlier lenses are chrome, later lenses are black. If possible test mount and focus Soviet lenses before buying them. If your Soviet camera Leica screw mount body breaks, it's probably cheaper just to buy another than to have it repaired. This table is an effort to give a quick overall view, so minor variations and rare limited production cameras have been left out.
Disagreements exist about model designations, production dates, and RF baseline lengths.
Personally I advise against building a Soviet camera collection, since it's unlikely to greatly appreciate in value during your lifetime. Just add a Leica screw mount to Leica bayonet adapter to your lenses, and they will work perfectly on your Leica M body. The Russian style script on the front top plate bothers my Western style eyes. Quality control is often very creative in soviet cameras, bouncing all over the place. In my opinion it is best to buy these in person, so you can personally evaluate the finder, film advance, and shutter, to make sure all is as it should be.