hi - welcome to the GMB

my opinion would be that it's not unique, unfortunately.............. this cut pattern is well documented and is shown on the Replacements.com site under Edinburgh Crystal in the Crystal section, and I'd have thought it unlikely that the metalwork - which appears to be either EP or EPNS - would have been made as a one off. Your piece appears to be a standard form of claret decanter, with nothing to suggest uniqueness.
There are more pieces than you can imagine that collectors find - especially cut glass from the middle third of the C20, or older - that remain as a single find without multiples turning up. Some pieces may well be produced in fairly limited runs, and of these many are perhaps exported and sold to the far flung corners of the globe never to be seen publicly again. No doubt many end up broken, so seeing just one is not unexpected for some of these older pieces.
A major problem affecting cut glass especially, is the lack of availability of factory catalogues with which to verify named patterns, which does lead to the speculation that if something can't be found then it must be unique. That's not to say catalogues don't exist, but being issued in very low numbers to start with, they become like hens teeth which means collectors are often unaware of their whereabouts. We have discussed the E. & L. and E. Crystal catalogues previously here, but I forget now what the conclusion was - they may well be in a museum somewhere. Some of the formerly large glass factories have passed through a variety of ownerships over the last quarter of a century and likewise the catalogues too, so not easy to say where these might now be. Certainly the Replacements site is an extremely useful resource for collectors for pattern names of cut glass - their coverage is very extensive. Could be wrong, but my opinion regarding the date for this claret jug/decanter is probably 1950s/early 1960s - but perhaps others may have a better idea.
It's attractive and a good piece either for use or simply ornamentation.
You might just confirm please that the mount is not hallmarked, and let us know if the base has the factory backstamp - thanks.
