Actually there is one more thing... When you kill dregs, the resulting drop is not cumulative. Each kill is an independent roll, not based on previous kills. It is possible (though extremely unlikely) to kill two dreg in a row, and both drop legendary engrams. So, no, you don't count all the dregs that gave you nothing. You were close, when you said the reward is luck... but then you said that once you recieve the reward it is earned. That is untrue. The chance was earned, and the result was luck. That doesn't mean that whatever your particular reward is was earned, only that you earned the chance at that particular reward, and got a lucky roll. Anyways, I wish you good luck, and good health. May all your blue engrams turn into legendaries. :)