The title is the lie. If the Author visited Auschwitz Museum, he would see the comprehensive photographic documentation. It leaked to the outside world much earlier than in 1944.

Polish underground had enough evidence of atrocities to produce the report as early as in 1942, https://en.wikipedia.org/wiki/The_Mass_Extermination_of_Jews_in_German_Occupied_Poland. Source material to these reports was brought from Poland to the West by a courier Jan Karski. He met with leading politicians in the United States and the United Kingdom, both as an emissary and eyewitness. This report was dismissed in the West as a Polish exaggeration. Even leaders of the Jewish community in the United States could not believe that it was the truth.