What other paperwork, if any, do you have from the original owner. As the car was driven in Europe, there would have been a registration document, number (license) plates, insurance documents, shipping documents, etc. My experience in 1969 was that Mercedes Benz of North America, included the cost of all these items in the selling price. It was also my understanding that they only sold cars for factory delivery, not with options to take delivery in other European locations.
If you go to the Technical Manual on this site and look in the Pagoda Notes Section, you will find in Pagoda Notes, Volume 10 Issue No 3, of September, 2016, copies of some of the above mentioned documentation.
I suppose it is possible that a U.S. person living in Europe could have ordered a car through a local dealer for export rather than through MBNA with factory delivery. In this case the temporary registration, plates, insurance, etc. would have been from the country where purchased. This was prior to the existence of the European Community.