Stefany, this may be covering old ground, but re: "...the hope that we could more accurately establish when the trading really started..."

Anna Weller of Big Bead Little Bead has a article on the "History of Venetian Glass Making" here: https://www.bigbeadlittlebead.com/guides_and_information/history_of_venetian_glass.php

References are noticeably lacking, but the article appears/may be a synopsis of several prior works. Possibly the references would be available. Under the section "Venetian Glass Making in the 15th & 16th Century", she states:

"Man-made glass was a largely unknown quantity in many of the new countries that these routes would open up. When combined with the high intrinsic value that Africans and Native Americans placed on decorative items, European merchants were set to make vast profits trading glass beads, metal beads, and porcelain beads for natural resources. This would give rise, to what can only be described as a Golden Age for glass bead production across Europe, centred on Venice and Bohemia, from the early 16th century to the close of the 18th Century.

In 1592, in order to meet this new market growth, the Venetian authorities allowed the glass factories to once again expand beyond Murano to many of the other islands in the lagoon of Venice, but in turn the ban on glass makers emigrating outside of Venice was extended to cover the whole Republic. To give an indication of this uplift in production, it is known that in 1525 Venice had 24 glassworks but by 1606 the register of glass bead producers alone had reached 251. By 1764 over two million pounds of beads were being made yearly in Venice alone. It has also been estimated that over 100,000 different Venetian glass trade bead designs were commissioned in Murano during this 200-year period, each with their own colour variations. Below you will see some examples spanning this period of production."