The pre-WW11 1920's Venetian bead necklaces that are distinctive are long, graduated and if they are on original thread they may be separated by small single-colour lampwork beads with equally large holes, and the necklaces I know of that time are continuous loops, they dont have a clasp.

One other early type is the liberty necklace- a long dangly necklace design with a tassell at the bottom and several parallel strands of rocailles which are threaded through a few impressively large beads, usually milles or fancy variations of them, to make a symmetrical arrangement. They are often shown and discussed here. Again no clasp.
However they break more easily. The thread is linen (called "cut garnet") and thin to fit the tiny beads. If you find a shorter one or one with a clasp it may have been rethreaded at a later date.

After those fashions and still before WW11 necklaces did get shorter but I dont recognise any style of short glass bead necklaces of the time as specifically Venetian, rather the Czechs were leading the trends at that time, or perhaps it was the French who created jewellery with the newer Czech beads.