Whilst I understand your scepticism, I really don't think that you're comparing like with like here.
The pieces that you allude to in Arwas's "Art Nouveau to Art Deco, The Art of Glass" pp 10 (not to be confused with the book I quoted earlier in this thread, for others benefit) are not the same beast at all.
They are both from more sophisticated and technically accomplished ranges produced by both artists, which admittedly give a nod toward what we're talking about here, but employ cameo decoration across the surface of the vases, which largely masks the technique underneath.
One of the difficulties here is that we are discussing illustrations, without the benefit of handling the item(s). Moreover, the items in question are rare, so inevitably there will be a divergence of opinion.
It seems to be a red herring to bring in an illustration of an item from a known manufacturer (Monart), which has a different finish with the enamel on the surface of the vase, and, apart from having patches of colour, bares little resemblence to the piece in question. Further, although there may be another piece by the same company that is cased , having random patches of colour and bubble decoration, there is no mention of crackling within the glass - as is shown with the piece under discussion.
Maybe I'm missing the point here, but is it that your just sceptical about the attribution, which I can appreciate and respect, or are we talking about mis-attribution by auctioneers? - which is an entirely different subject.