The C2A1 filter Canister was an upgrade from the C2 Canister. This has been the basic NBC / CBRN filter canister for U.S. Troops for many years now. These are military surplus filters, vacuum sealed, New Old Stock. The dates and lots will vary but they are all the newer style C2A1 in the plastic tub, not the older C2A1 filters in the metal cans (see separate listing).
These are government surplus that were stored properly to our knowledge. These are out of date but are still sealed. They are guaranteed from the manufacturer for 10 years from the manufacture date; however it is very possible that these are still perfectly fine. That is assuming that they continue to be stored properly.