It would be intereting to know....
.... if most of the German guards actually knew if Price was the spy.
It would make sense to not tell all of them, just the most trusted ones. Any sign of preferential treatment of Price, even inadvertently by one of the guards, might tip off the prisoners. You can see that in how quickly, and easily, they suspected Sefton.
Hitler! C'mon, I'll buy you a glass of lemonade.