Like I said, poor record keeping and forgotten stores of weapons and ammunition.
It happens all over the world.
This comment reminds me of a story I read about 30 years ago. When they were recommissioning the battleship the USS New Jersey in the early 1980s. They had plenty of ammo from WWII (Oh yes, we still have plenty of 16" ammo, because it is much cheaper to store them than to demilitarize them. And if the ammo is stored in a stable condition they have an unbelievable shelf-life.) but they were worried about barrels for the 16" guns. The barrels have a pretty short shelf life when you actually use them. And there was no manufacturing equipment to make new 16" cannon barrels. The Navy decided to continue working on recommissioning on the ship and build new machinery to make new barrels (which would take a long long time), assuming that they had some time before they wore out the current barrels. Without any prodding, countries all over the world were asking if the US wanted some prepositioned barrels that had been abandoned after WWII. Within a few months, the US Navy realized that they had more barrels than they could ever use.