I did know some of this -- I think the first feature film that actually engaged with the reality of concentration camps was The Stranger in 1946 -- but not the details about the war propaganda! What was the book?

(I don't let this book off the hook in this case, because one of the characters actually has seen the concentration camps, but I do wonder if its choices stem from sort of a similar impulse; 'let's show how horrible the war was for Obviously Ordinary People!')