You wrote that "they were incinerated along with the hundreds of thousands of Japanese civilians", which implies that at least 200,000 Japanese civilians were incinerated in the bombings. The 129,000–246,000+ killed figure you cite covers 2-4 months after the bombings. I am confident that no one was incinerated 2 or more months after the bombing.

Wikipedia gives an immediate death toll of 70,000–80,000 people, of whom 20,000 were soldiers for Hiroshima and 22,000-75,000 people for Nagasaki. This is far from hundreds of thousands of incinerated civilians.