>>bookof+(OP)
I believe the idea that China’s population was overestimated came out of the COVID vaccine rollout. Supposedly, the central government asked local officials how many doses they needed and then sent money based on those numbers. That gave some people an incentive to inflate the figures to get more funding. Later on, when the government looked at school enrollment numbers, they noticed there were way fewer kids than the number of vaccine doses that had been requested for children.