I've found that the cases generally come as an 'a' set , a 'b' set, and a 'c' set. I have bought two cases before and found that I got exactly 2/3's of the rares, and 4 of all commons, 2 of 2/3rd's the uncommon s, 1 of the last 1/3.
Sadly it seems you boxes weren't taken one after the other.