I Ran BT many time for DS Points, one run i would get one Lot of Drops, the second run another Lot of drops -
IE (1)single blade Lightsaber, (2) Doubblebladded saber) (3) back to the single blade Lightsaber,
Other drops i believe are set to drop after x amount of That mob has been killed ~ 100- 1000-10000, and so on, Just depends on who is killing said mob when x number comes up.