The overlay is definitely Murano. These do turn up from time to time (on eBay and elsewhere) with a poor quality 'Baccarat' logo etched on the base, by person or persons unknown.
The harlequin design first appears in the 19thC, in Bohemia / Alsace /Belgium. I suspect that Salvador Ysart (and Paul) saw examples when they were in the Paris area, before they moved to Scotland. Likewise with "Ysart" sulphides, and fountains / spiders. It is hard to say where your harlequin weight might be from, without seeing a close-up of the canes, and the base - but there are far more from Northern Europe than from Scotland. Sadly, there is a tendency for weights that look not quite right for Ysart, but actually come from Belgium / Alsace, to be labelled ' Rare or unique Ysart' by their proud - but deluded - owners. No names, no pack drill....