Canis Pugnax -
Send some photographs of your bottle to Christine - Diageo Archive Manager: Christine.J.McCafferty (AT) diageo.com
Make sure your photos clearly show each label and the closure being used, as well as a general shot. This will enable Christine to date the bottle as accurately as possible. If the bottle is as old as it appears, she does NOT recommend drinking the contents. Diageo's Technical Department have advised that whisky is at its best for 10-15 years - it may not go off, but it might lose its flavor if it is any older, especially if it is pre-screw cap!
Good luck - keep us posted!