Easy. Germans (being Germans) kept meticulous records (at it was actually in the neighborhood of 5.8M to include many other "untermenschen"). Years ago whilst in college I saw the official German records captured (the National Archives have a bunch) and no doubt in my mind they waxed that many.
A good principle to guide me through life: “This is all I have come to expect, standard lackluster performance. Trust nothing, believe no one and realize it will only get worse…”
