(a)      In this subtitle the following words have the meanings indicated.

      (b)      "Payment date" means the date of the Commission's check.

      (c)      "Proper invoice" means an invoice that contains the contractor's federal employer's identification number or Social Security number and the contract or purchase order number or other description of the contract and that contains or is accompanied by such substantiating information and documentation as is required by regulation or contract.

      (d)      "Receipt date" means the date that a proper invoice is received by the Commission.