The HC blog has an article on the number of Jews before the war. Several Nazi sources (and other sources) were used. According to them, the Korherr Report puts it at around 10 million and the Wannsee Protocol at 11 million (the same number Goebbels gives in his diary). However, they say that these sources overestimated and that the real number is 9 million (or 9.3 million to be precise) using other sources.
https://holocaustcontroversies.blogspot ... ve-of.html
So it looks like these 2 Nazi sources aren't completely reliable, if we are to take what they say. I do wonder how we can be sure of the reliability of the other sources though.