Say you're a juvenile offender of some kind -- some minor disgrace, but serious enough that you were sent to an institution with a locked door for a while.  Let's assume that after a certain amount of time (ten years?) your offense has been expunged from public files.  From your perspective, as a fine upstanding citizen who gets haircuts and takes a lunch to work, you have a clean record.

Now say you decide to change jobs.  You see something advertised that looks just right, and you decide to take the leap and try.  During your first interview with your prospective employer, he says to you "When you filled out this form for us you said you'd never been convicted of a crime.  But that's not true, is it?" 

What happened was that your record, when it existed and when it was public, was copied down in some way by (or maybe even sold to) a commercial company.  Why not?  It was available at the corner courthouse.  Although the public record was changed after ten years, the privately-held record persisted.  And now it has come back to life -- to your life.

You don't feel as if you were lying to your prospective employer.  Your lawyer told you those ten long years ago that your record would be clean and you would be free to start fresh.  But there's this guy across the table from you who paid a company to check up on you and now no longer trusts you.  You won't be getting that new job.

What's the right policy for something like this?  It can't be the right answer to make all public records secret.  There are good reasons to have the records of court procedures be public. Nor does it seem feasible to have all data tagged in some way so that it can be yanked back automatically when it ceases to be part of the public record.  Information wants to be available to be aggregated, and generally that's a good thing both for information and for people. 

It would be good if employers and educational institutions and insurance companies and other deciders didn't use datamined information in isolation -- if the guy across the table for you asked a few more questions, he'd get the whole story and probably wouldn't be as worried.  But people will always make decisions based on too few data points.

I don't have an answer.  My intuition is that the social risks of locking up information exceed the benefits of doing so.  But if you're the person trying to get that new job, you probably don't share that view.