US SSNs used to be that way. The initial prefix was based on where you applied, and the last four were shown like it was nothing (Boeing used my last 4 as part of my UNIX account ID). Instead of 5-9 digits of entropy, you're down to just 2.
I still don't get why anyone would ever want to treat SSN / national ID numbers as private information. They're usernames, you give them to so many people all the time and they're printed in so many places plain that it's ridiculous to think they should be used as a secret for authentication.
