Well, simply put, there are nineteen new blades, most likely any enemy in shallows can drop legendary. The clue said "looking new blades", any blades.I have read the names of the six and/or seven new bosses a few times and in different combinations and don't see anything that seems to be a clue or supporting something that you said. Am I missing something in their names?
Don't be surprised if legendary drops from anything. Like sprouts.
GL