The problem I've always had with the world of the Witcher is that I've always assumed that the main countries of the North were close to the size, if not a little smaller, of similar countries of late medieval Europe going by their population, technology, culture. However going off of that fact that Nilfgard is so far south and it should really be closer in culture so Spain, southern Italy or the Middle East.
So if they're the size of Belgium, Switzerland, Austria, etc., they should have been swallowed up by one another a long time ago. There never was a lot of smaller countries right next to each other, they'd always be swallowed up a large empire (currently happening) or one would take over the others. Ard Skellige is simillar to Viking culture and climate, but if so that would make Kovir and Poviss too far north to be important because of the severe cold wouldn't allow for larger populations.