NBC suits come in special airtight bags for a reason. They have a fairly short shelf-life after they are opened, even if not exposed to chemicals (less if they are). Most people are not aware of this, but just having a chemical suit sitting around exposed to the environment in a box somewhere will slowly deteriorate its protective ability. The military considers chemical suits and filters short-term consumables, because in any kind of real deployment you would throw them away pretty regularly, even if you weren't exposed to chemical weapons due to their rapidly deterioriating performance. Note that the same goes for gas masks. If you have one sitting on the shelf for years, the filter will be nearly useless. You need a supply of filters in the factory packaging (i.e. sealed canisters) that you can swap out if you need them.