Some economies, like New Zealand/Aeoteoroa were not populated until 1200/1300 CE which would be interesting to see in the stats. Other economies populated as translocation/transmigration of the population of other places wholesale. Indonesia had this, at scale. Millions of people moving. Hong Kong. 1949 partition in India caused massive shifts between two economies. Do we discount this happening in past times?
Estimates of population based on the number of individuals reported killed in battle would be very culturally informed. I have no idea how many camp followers a hoarde has, facing off the Roman army in Farther Gaul or Spain. How do you estimate population under migratory communities in steppes, or climate change effects in northern Europe?
It feels very guesswork-y
I liked the circularity reference. Easy to buttress yourself in a chain of references to peer review legitemacy, so economy estimates inform population and vice versa? use economic indicators when you don't have pop stats and don't ask too many questions where they came from!