War stock is lifed and batch tested. As long as the test samples exhibit the same success rate as the initial proofing tests then they remain good to go.
As failure rates pick up and maintenance becomes uneconomic then they will be withdrawn from service.
In the case of your individual with his prize possession then you are right, possession is worth far more than its use - until the moment went use overcomes possession.
OK, it's out of date. Are you going to fly by and be the test target?
Your 9mm Pakistani bullets sometimes failed to reach the target 15 m away. Would you stand happily at 30 m and assume it was impossible to hit you?