Generally speaking, if a bow's weight is marked at a length other than 28", it just means the customer ordering the bow requested the poundage at his or her draw length. In other words, the bow was a custom order.
Most bows gain or lose about 3 pounds per inch. A bow marked 60# @ 28" could also be marked 57# @ 27" or 63# @ 29". The bow would be exactly the same, the only difference being the marked poundage at the specified draw length.