For Excaliburs, you can determine the approximate year of production with the serial number on the back of the guitar. The first two digits are generally the year of production. For example, 9700064 means the guitar was produced in 1997; 0200089 means it was produced in 2002. This is not always 100% accurate, especially for guitars with black hardware. The real date is stamped on the neck and in the body neck pocket.
For the Excess series, you have to unscrew the neck, the date is stamped on the neck heel.
Other models prior to 2010 (neck through guitars and basses) have their year of production located under the Bridge Pickup. You can also look date your instrument here: Date your Vigier.