I'd suggest that the Oxford museum's conclusion is probably what most of us would have suggested - the shaped outer rim, the translucence, the colour, the gilding etc., and yes would agree further information probably a non-starter.
You might try the V. & A. in London - the glass and ceramics dept. will always offer opinions if you send them emailed pix etc. I had some chat with them recently over something though I've now forgotten what it was. They might take a week or so to reply, but get back to you they will at some time, though suspect their response may be no more specifically detailed than that of Oxford. I forget the lady's name, but do give them a try.