Due to the hukou system, 60 years of migration to cities from the rural countryside is not recorded by the official Chinese census. Migrants continue to be classified by their rural hukou and counted in the official census as residents of the rural area from which they came. Even the children of rural residents living in a city are counted as residing in the rural area with which their fathers family or grandfathers family was classified in 1951.
The second article is more interesting, and it does seem to support a potentially higher population for China then the official census records. However, there are few important qualifiers on that. First, they estimated the population of china to only be 22% higher than reported, not 100%. Second, if I am reading that study properly, they are claiming that many national census reports around the globe are too low. By their estimates, Brazil is under-reporting by 19%, Turkey by 40%, Canada by 32%, Thailand by 26%, and so on. Even the US population is actually 7% higher in their opinion. So this is less a case of China conspiring to hide their population, as it is census results globally being inaccurate.
As I mentioned, the real analysis was done with grid counts of the population though satellite imagery. I will see if I can get a hold of Smith. It may make take a few days with my schedule and I don't have his email address in my current contact file.
Do you ever wonder why China put so many of the huge ghost cities out in the middle of nowhere? A lot of those cities make no sense when analysts try and compare the official government line with their actions. I read a piece a couple of years ago, that the Chinese have something like 2 million more rural peasants moving (or trying to move) the big cities for jobs and a better life than the cities are capable of handling. There is supposedly a lot discontent with the rural population and the meager existence they have.
I did some searches on population grid counts and Chinese underestimating. Didn't find anything. As I mentioned, the piece was written sometime in the 90s and may have been before the internet (and search) became of age.
Chuck passed a long this link: Chinese population may swell to 1.5b
Follow the comment's links from the article.