I have worked on a few with it, there is a hole in the rear panel and in the alloy trim panel, a square rear fog lamp is fitted, seen it on 1971 cars but unsure when they stopped fitting it on RHD.
My 74 has it under the bumper…unfortunately nearly all pictures I have of RHD E9's are from the front. I'll have a look through though to see if I can find any pics of cars without it under the bumper.