I was thinking, just the basic: Total population, Male population, female population and like an estimated population.
Forth, we could use that and update it. New Terrance isn't on the list.
With any census, there is going to be gaps and people unaccounted for.
I am more worried about the player nations first. We can then go from there.
I too think some nations have a pretty hefty population, granted some nations should be heavily population. Maybe after looking at the data we can come up with certain guideline for population sizes, ex. Major underdeveloped nations should have relatively high population (or birth rate) while more modern nations should have a relatively decent size population depending on the size of the country (and a birth rate that is stabling out). But these are things we can discuss after the census if we deem necessary.