There's usually a Mailed copy, so who was the forwarded address for that person?

What about banking? SS is often a direct deposit function. And even then, the amount doesn't change other than the COLA, which is only once. You should be able to reconstruct the year from the bank statements, assuming you also know their Medicare cost. Who has those statements or that access? A proof of survivor can be provided to the bank; I had to get nearly 2 years of statements, for a client.

And there would be an online account, if one was established. As long as you have their password, of course. That's what I use when wrapping up a person's life = log into all email and online accounts to close out, cancel, delete, etc.