Receive COR entries from your ACH operator in your daily returns file; COR entries carry a change code in the addenda record (C01–C09) and the corrected data in the addenda information field
Parse the addenda record: field positions 4–6 contain the change code; fields 7–44 contain the corrected data in a fixed-format layout that varies by code (e.g., C01 = corrected account number, C02 = corrected routing number, C03 = both)
Update the stored bank account data in your system for the affected originator/receiver pair using the corrected values before the next origination
NACHA rules require that you act on an NOC within a defined number of banking days before the next origination to that account; check current NACHA Operating Rules for the exact requirement rather than assuming a specific number
Log each NOC with the original account data, corrected data, change code, and the date actioned; send a report to the originator so they can update their records if your platform acts on behalf of originators
For C07 (incorrect individual identification number) or C09 (incorrect individual ID number), notify the originator that the consumer's identifier in their system does not match the RDFI's records
Known gotchas
Originating a transaction with the old account data after receiving an NOC is a NACHA rules violation and can result in fines; your origination pipeline must check for pending NOC updates before submitting
C-code addenda field layouts are position-sensitive; an off-by-one parse error will silently extract incorrect routing or account numbers — validate corrected routing numbers against the ABA routing number registry before applying
Some NOCs carry corrected data that is partially correct; verify the full corrected account details with the originator or receiver before applying blindly, especially for C03 entries that change both routing and account number simultaneously
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