If I were a rightful leader of all Nigeria I would make sure those numbers would never be accessible for westerners as it’s the fist thing you need to know when you decide to wage war of any kind against some people.
You need to know military, not population size (how quickly can a militia be raised, how long can it be sustained, how well they are armed, who can be persuaded to defect, etc.). This is related to population size, but not linearly.
Population counts get only interesting for military and tax potential during administration of a territory.
GP's point is valid, though, imho.