A borrower does not have one credit file. Separate agencies each hold their own record, and those records routinely disagree in ways that change the outcome of an application.
Reporting is voluntary, not mandatory
Lenders choose whether to report an account and to which agencies. There is no obligation to supply the same data to every bureau.
Some lenders report to all the major agencies, some to one or two, and a few to none. Smaller and specialist lenders are the most likely to report narrowly.
An account that appears prominently on one file may therefore be entirely absent from another, which alone can produce a substantial difference between them.
Timing creates disagreement even with identical data
Reports are submitted periodically rather than continuously, and the submission dates differ between lenders and between agencies.
A balance paid down last week may be reflected on one file and not another for several weeks, so the same account shows two different balances.
Because balances feed utilisation, which is a significant scoring input, a purely timing-based difference can move a score without anything real having changed.
Matching errors put data in the wrong place
Agencies assemble files by matching incoming records to identities using names, addresses and dates of birth. The matching is probabilistic.
Common names, shared addresses and family members with similar details produce mismatches, in which an account attaches to the wrong file or splits across two.
These errors persist because nothing surfaces them until an application is declined, at which point the borrower is examining the file for the first time.
Scores are not comparable across agencies
Each agency uses its own scale, so a number from one is not equivalent to a number from another. Ranges and midpoints differ.
Lenders also run their own scorecards over the raw data rather than using the agency's consumer-facing number, which is a marketing product rather than the figure used to decide.
Comparing scores between agencies therefore measures the scales more than the borrower, which is why the underlying data matters more than the headline figure.
Why checking all of them is the point
Because a lender may pull from only one agency, an error confined to that file is enough to cause a decline while the other two look fine.
The correction process runs through the agency and the lender that supplied the data, and a correction with one agency does not propagate to the others.
Access rights, dispute procedures and retention periods vary by country and change over time, so the local rules determine what can be required and how quickly.