Wiki Tricare As Secondary Payor: Eligibility Started After SOC

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Hello! I am working on billing Tricare as a secondary payor for a patient. The patient has an start of care (SOC) from earlier in the year, but didn't become Tricare eligible until a few months later. We are a Medicare certified provider and must bill Tricare episodic.

I am not sure how to start my billing for patient responsibility though: Do I put the SOC on the RAP/CLA as the actual SOC date, or do I put the SOC as the day the Tricare became active? I think I remember something about this in our training for Medicare as secondary, where the SOC should be the start of the payor eligibility.

If anyone has any insight I would be very grateful! Thank you!