Square Bottle Dewar's

I have found several bottles of unopened Dewar's 12 year old blended whiskey. The bottle is green glass, it has a square shape, (not round) , the label reads...
"Ne Plus Ultra" the very finest Scotch Whisky of Great Age. Specially Reserved and selected, John Dewar & Sons Ltd, Perth Scotland. 25 ounces.

My question is... when was it bottled? And can you place the age of the Scotch 12 years beyond this?

This bottle may have been purchased in Paris.

Would this be prized by a Scotch affectionado? Or should I open it up and have a taste? (I would hate to drink a bottle that could make a mortgage payment for me) Please let me know if you can shed any light.

Thanks, -cmwiggle-