Not quite true. All of you have both at least until model year 2001.
In reality, both the left and right hand light units have rear fog light bulbs installed in them. But under the Euro law, it is only wired to light up on the driver's side. This is done by simply not putting in the power wire from the light socket to the connector during assembly. The Euro law was passed many years ago because people got confused when both sides light up. They cant tell the side of the car and it looks too much like brake lights with a malfunctioning 3rd brake light.
I modified my 97 E36 to light up both by putting in a simple wire across both the left and right hand units. I later located the power connector and replaced the wire with a short wire from the light socket to achieve the same purpose.
I did it again on my 2001 E39.