For a minute i thought you were talking about Elon and was completely following.

Ah, so data exchange between databases is a slightly different matter. First, I would recommend against using ssn as a number you exchange back and forth to sync data, as it exposes you to a greater risk of data theft. However, forcing your internal DB keys onto someone else is a a synchronization nightmare. Your internal data schema might look totally different even for the data overlap you might have.

My usual suggestion would be to assign a random uuid to each person and then just agree with each other on either which system creates new records (originates ids) or which system has priority (is the system of record) for people if there’s a collision. Ultimately, you’d end up needing to compare names and addresses or phone numbers or birthdays etc. to unify records anyway. SSN is an easy cheat that gets you a lot of the way there (for Americans born after 1935) but like I said it’s a security/legality risk and you still actually need to check that other stuff to verify anyway.

There’s a reason why systems that join person records together is big business (mostly for advertising!) It’s tricky stuff.