You obviously saw the interview with the Chinese lady. She makes a mistake in her assumption though.

She assumes birth rates couldn't hit ~5 per woman due to famine and CCP 1 child policy over the 50 years from 1950 to 2000 but multiple different data sets has the fertility rate of China between 5-6 from 1950 through to the 1960's. That alone is enough to eventually get the population from 500m - 1 billion, even including the famine and 1 CP.

I do though, think that many countries are adding or subtracting values to suit their own agenda. I dont believe India has more than China, for example, as I can't imagine 900m are living rurally.

Papa New Guinea's is an example of census data is certain to be under-reported. They claim 10m people but they are a nation where the majority of people, unlike most countries, actually do live internally away from the coastal regions due to the fertility of the land in the central mountainous regions. The issue there for those that want to collect data is that those central areas can only be accessed by navigating tough jungle or helicopter. One data set has the population closer to 17.5m. Almost double the reported census

So while I do think there is mis reporting, some honestly and some dishonesty, id say there is still between 6.5 and 7.5 billion people.

Anyway, what's a billion between friends 🤷‍♂️