before i purchase and pick up in tinley park, what is the expiration date on the box. how long is the cartridge good after expiration

I picked up a 21 box on 8/6/2020. the expiration date on that box is June 2022. I'm told that the cartridges hold up really well as long as they are in their packaging. I've bought cartridges now and then and held them months before opening the packaging. I recall getting a 21 and a 22 sold in one package and not needing both at the same time so I held on to one until I needed it. I've never had any problem when I've waited to use a cartridge but we're talking months here not years. I hope this helps out.