The gridded population tools I've used, including Worldpop, seemed to start with the national census data. Only with that do they use the various other measures

The gridded population tools I've used, including Worldpop, seemed to start with the national census data. Only with that do they use the various other measures as a way to subdivide the census data administrative units. I'm not sure if any of the mentioned gridded population tools are substantially census independent. Haven't read the paper yet, but maybe that could be one reason why methods are so similar.