That's how it works. RNG just calls upon a string of characters that correspond to a certain item. E.g. Raid Cloak corresponds to 10000-10050, RNG hits those numbers, you get the Cloak. Entirely possible that base loot I.e. Mouldering Shards are string characters as well and no gear rewards also. Let's say 10-300 with the numbers in between random other useless engrams. Blue between 301-8000 purple between 8001-9999. So you beat Golgoroth and RNG rolls x3 You hit 255, 5487 and 7888. So you get Shards and 2 blue engrams. The thing is, RNG does not roll against itself. So if you rolled 5487, it doesn't check to see if you rolled that. It just rolls from 1-X again. So you can get 5487 on every roll. Now this is highly unlikely, but there are cases of it. So you can roll, 255, get your Shards and then roll below 10 the next two times and get nothing. RNG blows and it is more complex than that, but I don't think you want me to ramble anymore.