As mentioned above - a weight of this name was sold at the museum auction (lot 756), though without image in the online catalogue.
At the time I had copied the details of the ebay auction (for my personal use): images are a bit poor - but this is definitely the same weight as Mike's.
Now - at first sight - there are some discrepancies:
Mike's weight is clearly marked 1984 - but seller on ebay mentions 1985 as date of manufacture - but further down gives the inscription as "1/500 Cannes March 1984". So it seems plausible that the 1985 is a typo - the weight may have actually been issued in 1984.
But then we have a discrepancy with the edition size: 500 (stated on ebay) versus 1500 (marked on Mike's). Now - this could be another typo - or the leading 1 was too faint on the ebay weight to be clearly seen. So to me it seems plausible that the actual edition size was 1500.
At least I can confirm IBM: though the image of the certificate is unsharp, it can be read "Cannes March IBM". The designer line is not filled in. It further states "This is to certify that this piece is number 1 of an edition of ." - i.e. no edition size given: could it be that first an edition size of 500 was planned - but then IBM decided to order 1500 after all?
So there are a few open questions - but my final question is simple to answer
: Mike - may we use your images for the Caithness catalogue on ScotlandsGlass?