Under options C to E a Defined Cost is what the Contractor pays the Subcontractor in accordance with the subcontract, subject to some deductions in clause 11.2 (23). So the first port of call is to look at the subcontract contract.
If the subcontractor has overpaid according to this contract, then it would be a Disallowed Cost under the second bullet of clause 11.2 (25).
If the subcontractor has overpaid according to this contract, then it would be a Disallowed Cost under the second bullet of clause 11.2 (25).