Up until I read this thread and gave it some thought, I never realized just how much the 3rd edition Ravenloft campaign setting had managed to cut the populations of the domains.
I mean, in both the black and red box sets, it plays fast and loose, but the general sense is that the domains are significantly more populated than the 3rd edition hard numbers.
I think this largely boils down to the following line hat 3rd edition seems to have ignored or overlooked from the village sizes listed in the black and red boxes:
The Black Box wrote:Wherever a population for a city or village is provided, the number includes only folk who live within its proper boundaries. As a rule an equal number of people reside in the immediate area[...]
It also mentions that it doesn't give details/map icons for places with populations under 1000 (exceptions like the village Barovia not withstanding) and further mentions that most domains have scattered rural populations across much of their terrain.
So, the case of Darkon:
Ignoring Il Aluk (curtesy of the the Grim Harvest), the city population of Darkon in the first two box sets is 54,500, or about 109,000 metro population. That's assuming that all 25k residents of Il Aluk and another 25k nearby souls all die in the Requiem. That does not count small villages or scattered rural populations across the largest domain in the Core.
In the 3rd edition book, the same 13 cities add up to 58,700. The entire domain of Darkon is listed at 117,300. That's a mere 8,300 population GREATER than the metro population from the original settings. I suspect that the rural population of Darkon exceeds 8,300 people. I also doubt that all 50,000 people in and near Il Aluk died in the requiem...I might be mistaken, but if I remember right, the harvest stopped not too far outside the city's limits, meaning that while some 25k+ likely died in that incident, a few thousands of the outside population could have survived (Necropolis is listed at 26,800 undead population).
Falkovnia, however, is even more surprising.
In the original boxes, the metro population of Falkovnia is 60,000 people. 3rd edition book lists the entire domain's population at 64,300, with half that living in the cities. Considering there's tons of farms (Falkovnia is the bread-basket of the core) it seems unlikely that the population in the box sets is entirely tied to the cities, and a significant part of the population is found outside that 60k. To further imbalance this equation, 3rd edition added an extra town of 1,500 people that wasn't previously listed.
Despite the fact that the towns listed for the domains all have higher (or the same) populations, the overall domain populations don't make too much sense from this info, seeming to imply that the populations outside city areas are nearly non-existant. This might make sense in some domains, but in larger domains like Darkon and Nova Vaasa I would expect the rural populations to add up to fairly significant numbers.
Oddly, the exception to this is Richemulot, where 3rd edition added another 10,000 people to the population of Pont-a-Museau for some reason.
That said, I'm pretty sure the Dark Powers and the Mists screw around with all this anyway and the details were originally vague for a good reason. For starters, the Mists love to deposit new people all the time in domains with no seeming rhyme or reason. I wonder what the 'immigration' rate to Core domains is, courtesy of Ravenloft suckering people in.
But the biggest reason I figure the powers that be screw around with it all is Har'Akir. In the original setting material, it has ONE populated location listed as having fewer than 100 people. Its built on the only spot in the domain that has water, and there are no other people in the domain outside this single spot. It even goes so far as to point out that all the creatures of the domain live in the cliff's below the Pharaoh's Rest coming out only at night, that nothing lives in the open sands itself, and that all the creatures in the cliffs are predators. It ends with the statement "how they survive is a mystery." That is not a sustainable human population (see: genetics, generally), and there isn't the life in the domain to support the living predator's of the cliff...yet the domain carries on for centuries with no problems, just waiting for Anhktepot to wake up from his mummy's sleep and once again loath his very existence. Because the Dark Powers don't care about 'realism,' they willingly flaunt it all the time with the very existence of Ravenloft.
We've been around each other long enough.