Out of date or unserviceable ?
The decision to extend the life of the ejection seat pyrotechnics is an interesting one.
The original manufactures will have considered a number of factors when setting the limitation, these are likely to be based on the harshest military operation environment with a good measure of safety and a bit of allowance for the deep pockets of the military budget. Once you start operating the aircraft occasionally without the temp cycles of high level flight and store the aircraft in a comfortable environment the safe life of such devices is likely to extend, it is for those who extend the life of these devices to base this decision on reliable data.
It is vital that the black and white attitude to shelf life is not taken and the date on the packet is viewed in the light of current operational conditions as this can move the date in ether direction to ensure reliable performance.