If an employee is entitled to permanent total disability benefits and social security retirement benefits under 42 U.S.C. sections 402 and 405, the aggregate wage-loss benefits payable under this title must be determined in accordance with this section. The employee’s social security retirement offset must equal forty percent of the calculated ratio of the employee’s average weekly wages, as calculated on the commencement of the first, or recurrent, disability under section 65-05-09, to the current state‘s average weekly wage. Any offset calculated cannot exceed forty percent of the employee’s weekly social security retirement benefit. If a claim has been accepted on an aggravation basis and the employee is eligible for social security benefits, the organization‘s offset must be proportionally calculated. An overpayment must be recouped in the same manner as set forth in section 65-05-09.1. This section applies to an employee who becomes entitled to and receives social security retirement benefits after June 30, 1989, or who receives social security retirement benefits that have been converted from social security disability benefits by the social security administration after June 30, 1989. A conversion by the organization from offsetting an employee’s social security disability benefits to offsetting an employee’s social security retirement benefits under this section may not result in a decrease in the aggregate amount of benefits the employee receives from both sources.