Most Celestion chassis drivers have been marked with a date code (two numbers and two letters), denoting the exact date of manufacture. These codes are added on the production line and are found in different locations depending on the age (or type) of speaker.
Date codes are expressed in the form of two digits (representing the day of the month 01 to 31) and two letters, one being the month, the other being the year. What you need to do is
1. track down the code,
2. refer to the date code table that provides an accurate record of the codes used throughout the years.