think I've seen that remnant in the V. & A. gallery. If this were the date suggested, then a very substantial find - pre-Ravenscroft pieces are excessively scarce, and almost without exception would show either Venetian or Dutch influence in style, and may even have been made in those locations, and imported.
At this date almost certainly soda glass, crizzling was a problem - the very small amount of lead content making pieces feel lighter in weight than might be assumed. Presumable you won't get the typical lead glass reaction from the u.v. torch.
This funnel bowl shape is apparently more typical of Venetian influence than Dutch, and the thin stem also looks more akin to Anglo-Venetian. On this piece the stem/knop formation appears too simple for either origin, and your comments about the flat base would probably rule out Anglo-Venetian. The shears mark on the rim is of no use for dating, and occurs on many glasses over a very long period of time.
Would be great if this were c. 1650, but I have that sinking feeling that the copyists have been at work again.
Needless to say all of the above comments are taken from the books - perhaps Peter (Oldglassman) is able to comment.