I'm not sure? I'm thinking no later than the1920's. They only have these purity stamps. Stylistically they look late Victorian to me, but it's hard to say being they have no date marks. I'm pretty sure the price would have been higher if they had the word sterling on them.
On another note, I couldn't focus my loop on the tiny little mark that was deep on the funnel shape base. What I did was take it into better light by a window and focused the smartphone cam on the mark and then enlarged the photo in order to view the mark that is about 2mm square in size. That's good technique to use when you can't get a magnifier close enough to focus on something or don't have a loop on hand.