There are plenty of problems with the site but that some stats like marriage do not count dead newborns as unwed instead of invalid for the stat is not really one of them.

What age of death discounts someone as counting towards the marriage percentage? If a human made the website, there would be an answer to this question. That answer might not be published and might vary between datasets, but it would exist.

In this case there is no answer, because the percentage is just made up by the LLM. There is no methodology. Your answer is inappropriately anthropomorphizing the LLM by imputing a methodology onto its "data collection" process.

No anthropomorphization was required, I just looked at one of the sources on that section of the page and saw the statistic did not involve the number of newborns and so figured myself those facts could indeed be simultaneously true.

How do I know the methods described in the source were correctly used here? I don't, but I also wouldn't know that based on whether or not a human wrote the webapp. I'd know that by checking the method applied on the backend matches that of the source. If it does, it doesn't matter if it was generated by using every 17th letter of the dictionary - it'd either align or not.

Which source was that?

In my case it was:

Preston, S. H., Heuveline, P., & Guillot, M. (2001). Demography: Measuring and modeling population processes. Blackwell Publishers.

In GP's case I believe they are correct the Hajnal source is not relevant to the Yangtze Basin but reading the first page should have made it clear the facts could be simultaneously true regardless where the percentages came from or if they were accurate.

Again, there are plenty of problems with the site. That it was clear these facts can't all be true simultaneously was just not one of them.

This appears to be a general introductory demography textbook. I am surprised that you looked at it and it contains specific demographic tables about marriage rates at specific time periods? Perhaps I am misunderstanding what you mean by 'I looked at one of the sources and saw it did not involve newborn rates.'

I think it might be a simple misunderstanding, but one can never be certain :).

I believe we agree we haven't seen a valid citation for "the source in which 'x' came from in 'x%'" for this stat on the site. I hope the two of us also agree this is not the point I was disagreeing with.

Where I'm currently lost is why a demography textbook, which was a different citation in the same section, must be unable to explain dead newborns need not be counted in such a statistic on the basis the textbook was not also the source of the specific percentages displayed? That'd be like saying a statistics textbook can't explain how the median can be less than the mean on the basis it wasn't also the source for the numbers displayed.