A/P Voucher approval and audit

We are looking for ideas from others on processes to ensure A/P Vouchers are reviewed, approved, and not changed prior to payment processing in E1.

We start by utilizing the Pay Status field.  Our default value is set at 'C'.  We use  P0411S program to move the vouchers from 'C' to 'B' - first level approval, then 'B' to 'A' available for payment/2nd approval.  We have turned on triggers so data related to voucher entry and status change is recorded for audit purposes. 

Our question is about the voucher being modified before payment group is created and paid.   The P0411 program does NOT modify the pay status back to the default of 'C' so it remains at the prior approval level of B or A in spite of the data change.  This leaves us open to payment a voucher that was not reviewed again.