Compare to the total number of records, very, very few were destroyed in WW2. It's not like every building on the planet were burned down. And lots of people h

Compare to the total number of records, very, very few were destroyed in WW2. It's not like every building on the planet were burned down. And lots of people have their own records in family bibles/other books. Modern genealogy sites (and even general web searches) have (and still are) digitizing old records, news papers, graveyards, and lots of other historical records, and this data is being fed into all sorts of databases/AI/analysis tools, making really precise records of giant family trees possible, with original photos, handwritten notes, census data, and on and on. So there's likely a better, more accurate records of all of this, back hundreds of years, aggregated than ever before. I know in my case, it doesn't take long now to trace parts of my family back 400-500 years into ancient France (I'm in the US). The number of original records I can see is astounding. It's only getting better. And it's pretty easy statistically to count % of people making age 100 in countries or regions where records are very, very good, get a good model of how that works, including as many relevant variables as people want to study, and use that to get a good estimate of how many are in places where records are poorer quality. That is how science is routinely done.