Hi - welcome to the GMB

As you will probably know, the company no longer exists and the name was taken over by Waterford Wedgwood something like ten years ago, so details of past products are now difficult to access, although it's possible that Waterford do have paperwork still so always worth sending them an email. I could be wrong, but having looked at the screen it seems that pieces from the Calendonia collection are not that common?? - but believe there was a ships decanter with engraved 'leaping salmon' in this pattern - what is the shape of your decanter? - are you able to show a picture? Something I was unaware of was the fact that many pieces during the final years were etched rather than engraved.
Also believe that during the last few years of their existence, much or all of their production was outsourced to somewhere like Czechoslovakia.
As another suggestion, it might be worth contacting Malcolm Sargent at Royal Scot Crystal - in the London area I think - who was apprently one time chief executive at Ed. Crystal - always possible he might either be able to help directly, or at least put you on to another source that can.
Best of luck.
Would be interesting to know the source of the sellers information.