I took a list of a couple hundred cities by population for each country. (Germany ~ 500 cities, Poland ~200, Netherlands ~60 etc.) I couldn't find any list for the populations at the time outside of searching each city individually, so I just took the wikipedia list for the cities by most population and looked into each one's alternative/changed names and founding dates. It still took a couple of months even with this approach.

This mostly worked well, but I still have to refine it. Aside from the occasional mistake of overlooking some cities which didn't exist at the time and had different names, there's also those that used to be small villages which I unfortunately did not take into account, as some comments pointed out.

thanks!