A mixed file happens when a bureau merges records belonging to two different people into one report, and the usual triggers are shared names, similar Social Security numbers, a junior and a senior at the same address, or two family members with matching initials. What often gets missed is that the same identifying data is sold to specialty consumer reporting agencies that build their own files, so a mix corrected at the three nationwide bureaus can survive untouched at the agencies a bank, landlord or lender actually consults.

• ChexSystems — an account-screening agency whose file can block a checking account for reasons the credit report never shows.
• Early Warning Services — the other major bank-screening agency, which also runs the Zelle network.
• SageStream — an alternative credit bureau most consumers have never requested a file from.
• Clarity Services — a specialty bureau serving subprime and non-traditional lenders.
• Innovis — a fourth nationwide bureau routinely left out of dispute campaigns.
• MicroBilt — a data supplier sitting behind decisions consumers rarely see explained.

When you dispute a mix, dispute it everywhere the data went rather than only where you found it. Send each agency proof of your own identifiers and a clear statement of which accounts are not yours, and keep the letters separate so no agency can point at another one’s investigation. An agency that merges two people’s records and cannot verify the result has to correct it, and repeated failures to separate files after notice are exactly what juries have punished.