I've been thinking about this recently.

Since most vampires seem to have a set herd or a group of mortals they tend to feed on, wouldn't that put a kink in the population estimates?
This is further complicated by the addition of the circulatory system which has the expressed goal of getting blood to kindred who are willing to pay for it.

Most estimates seem to be based on how many mortals a kindred would need to blend in and feed without being noticed, but a kindred who has a group of 10 blood dolls could survive comfortable in a very small area provided they don't...