Zyklon was invented as a fumigant in 1922, and is marketed today under the trade name Cyanosil. Crematory oven technology dates back to the 1890s. But even if you pretend that the crematorium workers only worked a forty hour week, with paid vacation, that still comes out to just under 400,000 per year. Something is very, very wrong here. It is not crematory ovens that prove mass murder, but the fact that they built to such a capacity.
Nobody builds such overcapacity unless they expect to use it, or did use it.
The official records of deaths were false - because they did not take into account the people gassed immediately, without ever being tattooed and entered onto the books.