Details about the Grand Prix race in episode 4 Reichshöhenstraße (1938)

The tv (or whatever) speaker says 15 cars start in the race (it also looks like that on the picture) and Caracciola is said to have number 28 (by the bystanders but anyway...). According to Wikipedia there were 20 cars starting at the 1938 German Grand Prix at the Nürnburgring and Caracciola had number 10. Is it just a factual error from either source or is the sound and picture from another race? (Or just an inaccurate fabrication). Details, but it seems weird in a series trying to depict history.