Sadie, my car, German order, Germany delivery, left factory March 17, 1970, ordered in 1969 - has option code 462 on the datacard, She had the switch and holes in the bumper in the proper places.
Perhaps they are called "Autobahn lights" because, actually, they are used rather rarely because of the fog as such, and much more often during a regular daylight driving on freeway during the rain (in some countries in Europe it is compulsory).
I did a brief search on regulatory topics, but to find German regulations from the 60ies would require more time. I think this light became compulsory in the EU in 1990 (so was e.g. in Poland, outside EU at that time). But it is not confirmed. Compulsory regulation about the rear fog light in 1979 in Germany feels a bit early...