No, refrigerant will not go bad. As long as you have a fully sealed cylinder and there are no leaks on the cylinder you refrigerant will last indefinitely. The only risk that you have is if your cylinder or valve gets compromised. Other than that your cylinder is a sealed unit and will not deplete or leak any refrigerant over it’s life time.
There are many people who will purchase a few cylinders of refrigerant that is about to be phased out. Once they have they cylinders they will sit on them for years. They either want them for ‘just in case,’ or to potentially sell down the road when the price goes up.