(1) Should the medical advisors report and certify to the board of trustees that such disability beneficiary is able to engage in substantial gainful activity, and should the board of trustees concur in such report, then the amount of the beneficiary's monthly benefit shall be reduced or suspended at the discretion of the board of trustees.
(2) If the board of trustees determines that the disability beneficiary is in fact engaged in substantial gainful activity, then the beneficiary's monthly benefits shall be suspended.
(3) Should the beneficiary's earning capacity be later changed, the monthly benefit may be restored; provided, that the evidence substantiates the beneficiary's inability to engage in gainful activity.
(4) Any disability retiree who has not yet attained service retirement age may be required to report, on an annual basis, all income other than retirement benefits from this system, and should the board of trustees determine from this information that the disability beneficiary is able to engage in a gainful occupation, then the amount of the benefit may be reduced accordingly, at the discretion of the board.