Things like Comichron estimates and best sellers lists will never give you the full picture on book performance. Since we can't have Marvel's internal numbers or accurately find them elsewhere, the best way to measure a book's success is, as always, see how long it's been going. Since Carol's books have been consistently going for several years, we know that her books are successful. Since KSD's pretty long run kickstarted the trend, we know hers was successful. The same applies to any series long-running series that you might not think is blowing up the shops.