I think it is probably the same race - it would be extraordinary if the car carried the same number for two separate races on two occasions. I wondered if the car belonged to a different class within the same race, and was being overtaken by the faster cars, but I don't think so. The race started at 10.30am, and was in three classes - Rennsportwagen (sports-racing cars) up to 1500cc, Seriensportwagen (production sports cars?) and GT cars up to 1600cc, and the same again up to 1300cc. The fastest cars set off first, and the other two classes set off at 3-minute intervals.
The race number of the mystery car fits in with the numbers of the other cars in the photo, so it's one of the 1500cc sports-racers. It looks like it's early in the race, since they are still close together, and the leaders in works Porsche 550s have gone past the camera. A German-language site I have found has a few photos of the race, but nothing with the puzzle car. It's interesting that the car has Dutch plates, because the unidentified Porsche entries are all German or Austrian drivers.
The "certain site" most of us know about does not have an entry list or programme, and asks on their site for assistance in finding these details. I do not hold out much hope - I have had no response from The Nostalgia Forum. Surely someone in the happy family of motor sports historians has a programme ? My own collection is fairly extensive, but confined to UK events because overseas items are too expensive !