Leiden - disc chape for gladius?

[Tarbicus]

The so called Parazonium is in some cases a perfect representation of an ordinary Greek sword. There is no evidence that such swords were still in use, other than Hellenistic sculpture. The examples referred to by you look extremely stylized and unrealistic.
Personally I suspect that parazonium did not refer to a special type of sword or dagger, but to a particular way to carry it. That would be diagonally at the left hip. This is similar to the meaning of paludamentum: a cloak draped over the left shhoulder and arm.

Rob, are you over-complicating something that is far simpler?