At What Point Does a Brand Stop Developing Personas

At what point does a brand stop developing personas?

A) When the company has identified 8-10 personas
B) When the cost of finding information about a new subset of a persona is greater than the benefit of marketing to that subset.
C) When it feels like it has enough
D) It should not stop,for it should always look to further refine its marketing efforts.
E) Once it has exhausted the Social Technographics Ladder