I was taught in school (in the US) that most Americans did NOT know about the holocaust or the genocide of the Jews even though there were photographic evidence and testimony of escaped inmates circulating in at least 1941. I have to assume that once these rumors came out the Germans—who were no strangers to shouting "fake news" themselves, would have pushed a disinformation campaign... but I don't know. To draw a contemporary parallel—what is happening with the Uyghurs in China—might something like that have happened in the 1940s?