Usually if you pick up an object and it's not a trophy and you can't craft anything with it, it's a boss summon item.

Eikthyr breaks this because the item is both a trophy and used to craft something. The Queen breaks this because I don't think you can summon her with Dvergr steins, and you do craft her key, out of something that is otherwise useless. (Would be funny if you could use the steins to summon Haldor.) But otherwise...