I’ll add that there is a huge difference between the SSN database that the Social Security Administration maintains, and the list of SSNs that have been associated with a person. Especially because it is very common to change a single digit of your SSN when performing credit fraud - because they’ve already burned their real one. Some people will have dozens of SSNs attached to them.

IDA was very good at determining who a person is through the graphs that represent identities in our world (names, DOBs, phone numbers, addresses, SSNs, etc.)