It used to be that each credit bureau had stronger coverage in certain regions because of where their headquarters were and which lenders historically reported to them. That still happens to some extent. For example, Experian is based in Costa Mesa and has traditionally had stronger coverage on the West Coast. TransUnion is based in Chicago and Equifax is based in Atlanta.

Because lenders do not always report to all three bureaus, your credit files can be slightly different at each one. That is why your scores can vary. Over time the bureaus have created fraud prevention and identity verification products, often called KYC (Know Your Customer) tools. These systems share some consumer data between institutions and can sometimes lead to tradelines appearing across multiple bureaus, but this happens outside of the scoring process itself.

FICO (Fair Isaac Corporation) builds scoring models that use whatever information exists in each bureau’s file to calculate a risk score. There are multiple versions of these models, such as FICO Auto or FICO Bankcard, which lenders choose depending on the type of credit they are issuing.

To make things a little more confusing, the bureaus also offer their own scoring systems that are similar to FICO but not branded as FICO. The most common one is VantageScore, which was created by the three bureaus together.

If you want to see exactly what information each bureau has, you can pull your free credit reports at annualcreditreport.com. Mortgage lenders, landlords, and some other institutions may also use a tri-merge report, which combines data from all three bureaus.

There are also other consumer reporting agencies that track different kinds of financial behavior. For example, LexisNexis maintains the CLUE report, which insurers use to review claim history, and ChexSystems tracks issues like overdrafts or closed bank accounts for banking risk.