Charles,
As i said, i've been wrong before. You've handled far more Murano than I have, so I won't dispute the Murano attribution.
From a learning point of view for me, given that virtually all Czech and Scandinavian also have polished bases, what is there about this polished base that "screams" Murano? For example, Vas Vitreum did a fazolletto, seldom monochromatic, which has a polished base.
David