If it's on display, it's in perfect working condition
Plenty of times in fiction there's an odd occurrence when an item that's on display in a museum or privately appears to be completely functional, so that a character can simply grab (or perhaps enter when it is a vehicle) and start using it immediately. Of course, this is not how it works in real life. If you see a WW2-era nuclear bomb in a museum, you can bet it's not topped up with weapons-grade uranium and working detonation charge. Firearms on display might have their barrels completely blocked by metal, and so on. There are even instances where the actual age of a display item seems irrelevant to the working condition of the chemical, mechanical and electronic parts of the item on display. A specific example of this in fiction: Demolition Man: Simon Phoenix goes to steal firearms from a museum, the only place where they exist in the utopian society. He grabs weapons from display cases, and they all appear to be immediately functional and with plentiful supplies of ammo nearby.