Does the IRS actually know what everyone owes? I know it's true for W-2 employees, but what about everyone else?

I've always had this feeling that you could ask the IRS what they believe any given SSN/EIN owes and they'd be able to tell you (not that they would, but that it's already calculated somewhere). I don't know if this actually true though. I know almost all W-2 information is sent electronically. They know about most 1099 transactions too. But is all this information pre-compiled against someone's SSN, or do they only run that calculation as part of random audits?