Roman Glassware

[fwg]

Here's what I was wondering about -- how do we date the particular dates of the various glass inventions?

Just from the finds, since written sources are quite rare. The upcoming of different new 'invented' glass vessel groups (wich obviously require new techniques) within an aerea / time normally leads to the conclusion of the prior invention of the required technologies.

A lot of the sites mentioned here say that glass was invented circa 2000 BC in Sumeria, and was found in Egypt as well; but as far as I know all they're referencing are small transparent beads, which could be polished rock as much as molten glass production, so what actual glass pieces have we found from Sumeria?

It´s quite easy to distinct polished rock from glass, since the melting process changes the appearance and the thing we call glass needs some more ingredients in addition to silica, such as soda / potassium.
But if we neglect the (maybe unintentional) invention of glass beads, the early times of glassmaking brought mainly sand core formed vessels.

Secondly, the UPenn website claims that glass blowing was invented near the end of 1st century BC by some glassmaker in Jerusalem; how can we make claims with such a specific certainty,...

You can´t seriously make such specific claims. This might reflect the seriousity of this source...
;-) )