Does anyone actually have any links or evidence that China is overcounting its population?
For years the govt was worried about the opposite, and actually commissioned studies that showed the population wasn't bigger than speculated. They rely on census stats quite accurately in order to maintain a certain algorithm that's been used to feed 19% of the world's population on only 7% of its arable land (2/3 of the country is non-arable). There's even a Chinese name for that algorithm -it's been vital to ward off famines, wars, and to the plan of development for the nation.
Given the upheavals in economy, land usage (millions of acres of farmland losing out to growing development) and consumerism from the 1990s, it was last set at 120 million hectares reserved to keep it all sustainable.
In the 2010's China started importing food for the first time, which meant the algorithm was failing. There was a lot of speculation as to how an official population of 1.3 billion people was eating the equivalent to 1.5 billion - yes there were many undocumented children as a hangover of the one-child rule, plus many undocumented migrants, and increasing consumer intake - but repeated amnesties didn't reveal such a climb, neither did the world's largest survey industries that The Party operates. (On that note, undocumented migrants are still counted in the censuses, they're not fined, and their kids go to special migrant schools).
It took years to find out that the increases in wages and business meetings etc was the real culprit, not extra people. The tradition for Chinese banquets (where so much food is cooked the hundreds of guests can't possibly finish 20+ courses), thrown at every wedding, festival and business deal was haemorrhaging the food industry - enough to feed 200 million. They found out in 2013:
The Incredible Waste of Chinese Banquets
To this day banquets are now banned for govt officials and frowned upon at large, though they still operate covertly against 'Operation Clean Plate'. The country still budgets for an extra 200 million, still imports food etc, but it doesn't pretend that they're made up by undocumented mouths to feed.