And the light bulb finally went off in my head, given your last comments. The intaglio vase is topaz on the bottom, top, sides and inside, so I had assumed that it had been cased like a sandwich with a thin outer topaz layer and a thicker clear inner layer. But of course a staining of the entire piece would also create the same effect, and is much more likely. It is quite the expert job, as I had checked the piece to see if there were scratches, little splotches, or a missing spot of color that would indicate a stained piece, and the color is absolutely consistent throughout. The scratches on the base are not clear, but they aren't very deep. Even the pontil is topaz, which actually may be an indication that it was stained.
Also, even if it has an outer casing of topaz, you are correct that it would rule out Moser, since the Art Nouveau intaglio pieces have the inner layer of color, which is the complete opposite of this vase that has the color on the outside. I am not aware of modern work having the design cut deeply around the sides of the piece, in the style of the Art Nouveau deep intaglio engraving, but I wouldn't be surprised if there has been a resurrection of the style at some point, so perhaps Moser's attribution is correct.
I did send a photo of my applied glass fish vase to Moser for their opinion (attached). It is the standard blue crackle glass, with two blue applied glass fish that have been enamelled quite beautifully on the surface. I have seen these attributed to either Moser or Harrach. Moser replied
"On Friday I was informed from the Moser specialists that this glass vase was not manufactured by Moser glassworks either. The used design and colours correspond more to production in the glassworks in Nový Bor in North Bohemia but we are not absolutely sure about it." Harrach is in the north, but not where I would call the Novy Bor region, but more over to the East near old Silesia (Novy Svet), but then again, Moser did say they weren't sure, and perhaps crackled glass fish vases were done by more than the 2 companies?