Nonconformance rework on Sub-contract

We buy a PCB Isolation Board which is coated with a treatment with a shelf-life. When the shelf-life expires it can be sent back to be recoated for shelf life extension. These are place in Nonconformance and will be sent out for coating, the question I have is how do you prevent the received back PCBs on the subcontract PO without increasing on hand quantity of does the Nonconformance balance need to be DMR out?