First think about this :
some air conditioners or refrigerators can be used continuously for decades ? So does the refrigerant such as refrigerant R600a, refrigerant R410a have a shelf life? Is there any difference between the refrigerant in the bottle and the electrical pipeline?
The faact is: you can store refrigerants for as long as you would like. The gas will not go bad as long as there is not a leak in your cylinder. If your cylinder is completely sealed you can hold onto your refrigerant for years without any worry.