I have to agree with Ivo and Bidda.
The Nason stuff is from the 60's / 70's and is done with finesse.
The splodgy, sludgy, slurry, smeary Dalian stuff is slap dash, without artistry, of inferior quality and probably more recent.
The devil is in the detail.
Collectors (en masse) will eventually learn to tell the difference even if that the moment they can't.
As to Formia, I have a theory which I am not able to prove as yet so will stay quiet.