Like most non-organic things masks "expire" because the manufacture needs to not be liable after a certain date (after all, the manufacturer can't be realistica

Like most non-organic things masks "expire" because the manufacture needs to not be liable after a certain date (after all, the manufacturer can't be realistically held responsible indefinitely) and the institutions buying the masks are unwilling to take on the responsibility of determining the quality of their own stockpile so they just trash them and buy more. The military actively researches this kind of thing and knows exactly how long past it's expiration date many products are good for. I'm unaware of any other organizations that take on this responsibility.