The first time you do Kings Fall in a week, normal or hard, you are guaranteed at least Mouldering Shards for each checkpoint per character. Beyond this, there are no guarantees on loot drops, except hard mode Oryx will guarantee a drop. If you run hard mode first in a week, you will receive the drops for both normal and hard at the same time. Also, your mouldering shard guarantee only applies to one of those two rolls - at that point, the second loot roll can produce loot, but is not guaranteed to do so. https://www.bungie.net/en/Help/Article/12287