Please check me if I am wrong, but AFAIK, "M16" is the military designation and no M16s (or M16 lowers) were ever legally owned or sold on the civilian market. Prior to 1986, selective fire AR-15's were sold to police and some were sold on the civilian market, but they were not marked "M16". It seems common to refer to any selective fire rifle of that type as an "M16", but that appears not to be accurate.
Or am I about to be jumped on by thousands of folks who own M16's, M249's, Ma Deuces, 155mm SP guns, M1A1 tanks, etc.?