You're not alone in your pondering, Anita. (There's a song in there, I'm sure.) I've spent a few hours over the years looking for what the difference might be between bollicine and pulegosa and I've never found a satisfactory answer, which tells me that there isn't a huge difference.The terms even mean the same thing: bollicina is bubble in Italian and puleghe is bubble in the Venetian dialect. Venini: Catalogue Raisonne and Venetian Glass: An American Collection both give pretty much the same definition of pulegosa, a technique where bubbles are created by adding a substance such as gas/petrol to the glass. Nether gives a definition of bollicine, although the Losch site does and the defintion is pretty close to the pulegosa definition without mentioning gas.
I've come to the conclusion that the basic technique is adding another substance to the glass that creates a chemical reaction, leading to the formation of gas bubbles. The size and shape of the bubbles vary according to what you add to the glass. Gas/petrol creates a very frothy bubble glass, as you see in Murano pulegosa and in the 40's Skrdlovice glass. Other substances that I've hears been added are some sodium compounds, potato peelings, and pieces from an ash tree. I'm sure there's more. Another variation is caused by where and when you add the second substance. The gasoline/petrol is added to the the glass in the pot, for example. The second chemical can also be spread on a marver (not gas, of course) and picked up on the parison, which is then dipped in the pot. This creates the localized bubbles you see in some Scandinavian pieces.
I'm not sure about whether or not the glass being cased makes a difference. I think the early Venini pieces weren't cased, which led to the pitted surface you talked about Anita, but I've got some cased pulegosa. It also depends on whether pulegosa is the only technique being used on the piece. The early Venini pieces were focused on the shape and texture of the piece, so no casing. Other pulegosa had layers of colours or frit added to the pulegosa so they were cased.
I think you're right, Anita, when you say bollicine was often used in conjunction with the addition of inclusions or with sommerso, which might give us an idea of when we should use the term bollicine. But it doesn't give us a term that encompasses the range of glass with bubbles we see, unless that term is pulegosa.
Anita, and you thought you were the only one in need of a life! I think of it the mental exercise I need to prolong my life.