Certificates don't "expire" the way say, milk expires. An expired certificate is just as valid the day after its expiration as it was the day before, and a sign

Certificates don't "expire" the way say, milk expires. An expired certificate is just as valid the day after its expiration as it was the day before, and a signature that was made with the certificate is still just as trustworthy. Certificate expiration is just an indication that the organization that issued it wants more money to keep saying that it's valid. I'd have some concern if new firmware was being signed with an old certificate since there's been more time for an old certificate to find its way into the hands of a bad actor, but the company managing the expiration dates isn't in the business of tracking who currently possesses it so I don't really see much reason to pay attention to what they say about the date.