If any payment is not paid within two weeks after it becomes due, there shall be added to such unpaid compensation an amount equal to 20 percent thereof, unless the Commission finds that any required payment has been made as promptly as practicable and (i) there is good cause outside the control of the employer for the delay or (ii) in the case of a self-insured employer, the employer has issued the required payment to the employee as a part of the next regular payroll after the payment becomes due. No such penalty shall be added, however, to any payment made within two weeks after the expiration of (a) the period in which Commission review may be requested pursuant to § 65.2-705 or (b) the period in which a notice of appeal may be filed pursuant to § 65.2-706. No penalty shall be assessed against the Commonwealth when the Commonwealth has issued a regular payroll payment to the employee in lieu of compensation covering the period of disability. As used in this section, a regular payroll payment issued by the Commonwealth includes payments issued net of deductions for elected and mandatory benefits and other standard deductions.