I Google the claims about the population decline. There are some claims that the population was adjusted after the fact to reflect the imaginary loss of 6,000,000 lives. On top of this, the pre-war stats for Jewish population was pumped up a few million as well. That doesn't mean a ton of Jewish people didn't die or get killed. Just unlikely that the "6,000,000" figure is accurate. Also considering it's use in the past makes it less likely to be accurate.