Well, not necessarily. This is my mere assumption and not a fact but my logic comes to this conclusion. Since SSNs are not recycled, then ours is ours till the day of our death. Therefore, even if our SSNs llegally become invalid to use; the SSN itself is valid. So here's the interesting part, we could pretty much keep using our SSNs unless, whoever we provide it to, it goes through some sort of verification for usage validity.