With my current barbarian nation, my historic goal is to take over 56% of Northern Gaul.
However, the percentage owned, as indicated in the ledger, doesn't seem to match what I actually own. It's always lower (I checked for both the %age of provinces owned, and the percentage of the total population). For instance, when I owned half of the region, the ledger was telling me that I owned 27% or so. When I got all provinces except three, the ledger mentioned 56%. And now that I own all of them, it mentions only 75% (note that I've at least one unit in every province, so it's not an issue of control).
On the other hand, it's exactly the contrary for the "tax bonus" you get for owning the majority of the provinces in the region. When looking in "economic" mode, it was mentioned that I owned 50% of the provinces when I actually owned maybe about one third of them, 66% when I owned half of them, and now that I own all of them, it indicates.... 133%.
So, what's the deal with the %age of ownership in a region?