I agree with Allan: the base does give some clues (but may not be original), whereas the best information is from the design. Most Murano paperweights are identifiable by the style of the millefiori canes, but the frequent use of aventurine in a design often indicates Murano too. I do not think the base gives any clue as to which of the many Murano factories may have made the piece (unless it has the name etched on it, or a label
Just to add to the confusion, I have seen a few Murano paperweights with a concave polished base, and also a couple with an 'unfinished' base that showed a depression and pontil scar.
There are a good number of Murano images in the 'Murano project' pages of my website.