Mark

Actually, let me try this without documentation.....
 
Image   and explanation from from Aeronautics Guide
  
     
  
Discharge Cartridges

The service life of fire extinguisher discharge cartridges is calculated from the manufacturer’s date stamp, which is usually placed on the face of the cartridge. The cartridge service life recommended by the manufacturer is usually in terms of years. Cartridges are available with a service life of 5 years or more. To determine the unexpired service life of a discharge cartridge, it is usually necessary to remove the electrical leads and discharge line from the plug body, which can then be removed from the extinguisher container.

I'm guessing you're complying with fire bottle time change requirements. The aircraft records "should" state the previous bottle change date, but they usually don't show information on the squib which is not a serialized part and may not have a date stamp. There is no positive way of knowing the age of the removed squib without a date stamp. It is normally recommended to install a squib with one that has a known shelf life.

I'm somewhat puzzled though, most of my bottle changes in the corporate world and commercial side have always had the squibs installed from overhaul.

I would practice extreme caution when dealing with squibs and fire bottles.

(The removed squib should be discharged before disposal.)