Your question doesn't state which main Option is being used however I can answer for A or C/E.
If it's Option A then your focus only needs to be on what work has been completed and there's no need to get into what the Contractor may or may not have paid a Subcontractor. If the work hasn't been completed then the Employer has no liability to pay for it - refer to definition of PSPD at clause 11.2(17).
If it's Option C or E then it's perfectly reasonable to ask the Contractor for evidence of amounts they are claiming they have paid. Both the definitions of Defined Cost at clause 11.2(5) and PSPD at clause 11.2(18) refer to amounts paid by the Contractor. Further clauses 52.2 and 52.3 require the Contractor to keep records of Defined Costs and to allow the Service Manager to inspect accounts and records.
If it's Option A then your focus only needs to be on what work has been completed and there's no need to get into what the Contractor may or may not have paid a Subcontractor. If the work hasn't been completed then the Employer has no liability to pay for it - refer to definition of PSPD at clause 11.2(17).
If it's Option C or E then it's perfectly reasonable to ask the Contractor for evidence of amounts they are claiming they have paid. Both the definitions of Defined Cost at clause 11.2(5) and PSPD at clause 11.2(18) refer to amounts paid by the Contractor. Further clauses 52.2 and 52.3 require the Contractor to keep records of Defined Costs and to allow the Service Manager to inspect accounts and records.