The claim arrived after the payer filing deadline, which can be as short as 90 days from the date of service.
These usually trace to claims that sat in a rejected or draft state nobody was watching, or to a payer change discovered months late. The denial itself is rarely winnable; the fix is upstream.
A claim rejects at the clearinghouse in January for a bad member ID. The rejection report goes unread. In September someone finally notices the unpaid visit, fixes the ID, and submits a clean claim, which now denies CO-29 because the payer filing window closed months earlier. The claim was never late; the follow up was.
Medicare requires claims to be filed within one calendar year of the date of service, per the Claims Processing Manual, Chapter 1, section 70. Many commercial contracts allow far less, sometimes 90 days.
Cervica ages every claim from submission and surfaces claims stuck without a payer response long before deadlines pass, which is how CO-29 becomes rare instead of routine.
General information for billing teams, not legal or payer specific advice. CARC definitions belong to X12; payer policies vary and control. Verify against the payer contract before acting on any individual claim.