Other people have mentioned this… but it’s been established in policy that the SSN of a deceased person is not PII. There are a ton of different ways to get the SSN of someone who is deceased.
They aren't "public" but if you have a good reason, the govt will let you see the list of dead people SSNs. It's one of the first things checked when you're trying to open a line of credit because it's so easy to verify.
