Find out what the top three credit bureaus -- Equifax, TransUnion and Experian -- are saying about you. It's likely that they're all slightly different. Yes, different! Creditors don't have to report to all three credit bureaus, so they typically report to the credit bureau to which they also subscribe.

Nearly every consumer has an error on at least one credit report from one of the major credit bureaus, says Rhode. Credit bureaus generate your report on information they receive from your creditors; they don't verify.

Source:
http://www.bankrate.com/brm/news/cc/20011008b.asp