I would imagine they'd have to use new ones every once in a while. What I am most worried about is vendor's key becoming compromised (whether cracked or stolen

I would imagine they'd have to use new ones every once in a while. What I am most worried about is vendor's key becoming compromised (whether cracked or stolen), which means that a revocation mechanism is missing. Even with revocation implemented, such equipment would be rendered useless (I imagine vendor would have to cover for replacements).