You know how if you kill a delve boss, then kill the same one because it spawned in abnormally quickly, and when you loot it, there's nothing but a few pieces of gold?

Do leads drop at all, if this is the case? Where you're on cooldown?

Or do they only drop if the boss drops actual valid items: e.g, gold + soul gem + ornate item + intricate item + zone-related item?

Also, is this also the case for World Bosses?