I wonder if Vorderseite means that "this disc is for the front end of the driveshaft, not the rear end" ??? Gad, who knows.

Best approach to put this to bed might be to search around and find a good photo of an OEM-type that has the German wording "this side towards driveshaft" on the photo, then match the one you have to the hole configuration in that photo, and put it on.
Pleas let us know the outcome, for all our future reference.

Cheers,
DG