I've actually waited (while playing) with two additional cities, and still don't see the population updating ...
I am working on four cities in Viridian Woods: Gougin Valley, Matisse Plains, Rousseau Flats, and Monet Plateau. All cities are between 70k-110k. I built Gougin Valley and Matisse Plains first, and used them to found an archology. After it was completed, as expected, I started to see a significant uptick in the visitors to those two cities ... AND I can see the full population when viewing the archology from those two cities.
I then started Rousseau Flats and Monet Plateau. They both recognize the archology and are also seeing surges in visitors, but for some reason the archology only shows a population of 28K when it shows 1.74M as viewed from Gougin and Matisse. So the surges in population for those two cities is consistent with the population the game records.
I saw your answer above, but I'm still not seeing the game to update the population for the archology as viewed from Rousseau Flats and Monet Plateau.