Hi Glen!
Are you able to provide any more details of your bulb or maybe even a photo? Then hopefully I may be able to identify the date more precisely for you.
Such details as the country of origin, the precise wording any any other codes marked on the bulb would be very helpful. Also, does it have a small glass tip on the crown of the bulb, or is the shape more like a modern household bulb?
Best regards,
James.