Color, feel, look, even the amount of dirt in the bottom make me think it's early 20th century or before. I haven't seen any of Davidson's later glass (that I knew was there's), but I've handled a lot of other later glass. With the furnace going, the air is dryer in here, but I don't think it has that later tendency to attract water out of the surrounding air.
At any rate, it's headed to eBay tonight, even as much as I've grown to dislike eBay.
Thanks for the update on coding for this board. I know that just about every board is a bit different, but with some weather induced sinus problems, I haven't felt much like checking those fine points.
Forrest