Well done on finding the maker, Liz.
I think there could be a few reasons why your example is not signed:
- it might be an unmarked trial (or artist's proof) piece
- they may have forgotten to sign it
- it could be a "seconds", because of a flaw in the working, and perhaps not intended for release
On the point of it possibly being a "seconds", the base area of yours appears smaller (or at least, less precisely formed) than in the photo of the other one you found. Also, there seem to be less bubbles in the background of yours. These could, of course, be my own interpretations from the photos, which themselves may be at "substantially" different angles, giving a different visual effect.
Checking with GES would be a good idea.