Some of what you say points to the innacurracy that is inherent in the counting process. But it does suffer from several abuses of logic. For starters, 6 million is not an innapropriate starting number if 5.9 million Jews missing at the end of WWII. I understand you point about population projections. However, you overestimate it's effects, and you outright mug statistics when you compare it to the U.S. population (which is 50x greater). World War II was about a six to seven year event. From 1900 to 1914 the European Jewish population grew from 8.9 mill to 9.1 (approx. 3% over 15 years). then from 9.1 to 9.5 form 1914 to 1938 (approx 4% over 24 years). It works out to about .2% per year. So, any overestimation, due to the lack of easy baby making, would amount to 1.2% of (lets say) 10 million. This is 120,000. And then the Russians surely killed some Jews, but we have no evidence that it was anything as organized or thorough as the Nazi effort.
from the article: U.S. Jews block conference set to include anti-Israel professors