I'm pretty sure they do, however, specific set pieces drop at certain bosses, which is why if you're in vWGT and looking for SPC boots, you need to kill trash mobs, if you're looking for leg or belt armor, you'll keep farming the first boss.
Those dungeons with jewelry and weapons, the last boss is the one who drops those, which means you have a chance when killing the last boss for either a weapon, a ring / neck or a shield.
So if you want to farm, say, Vicious Ophidian jewelry, you'll try to rush to the last boss.
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