I'm not the best player by a long shot & I'm running a thief/assassin type without reading anything about how other people are playing theirs i.e. armour, perks etc. So, I've been learning as I go. I'm about 110 hours into the game.
So, I'm in New Fall Sanctum & I just killed a Dragu Death Overlord & his companion up on a platform in a room I'm pretty sure I could just sneak through, but then what is the fun in that. It took me several hours of die, load, rinse & repeat (see above) before I finally killed them, however there was NO loot on the Death Overlord...really? His normal Honed Great Sword was there on the ground, but he was not lootable...so, I did it all over...load, fight...die...repeat until I killed him again & again NO loot...The toughest mob I've come across so far & not one single piece of loot form him.
/sadface
EDIT: A save & load of the game made them lootable. Nothing fancy to loot; just some gold, but at least lootable.