First, the post is about blue chip ratio. So it is percentage of 4+ star players. It doesn't matter if one of them is a 5 star, as long as they are 4 or higher they contribute to the percent of blue chippers. Second, if there are the same number of blue chip players in two different years, yet the blue chip percentage is different, this implies the total number of players is different for those two years. With 4 blue chip RBs in 2018 with a 50% blue chip ratio, that means there were 8 RBs on the roster. With 4 blue chip RBs in 2021 with an 80% blue chip ratio, that means there are 5 RBs on the roster.