(a) There may be a provision as follows:
"Relation of Earnings to Insurance: If the total monthly amount of loss of time benefits promised for the same loss under all valid loss of time coverage upon the insured, whether payable on a weekly or monthly basis, shall exceed the monthly earnings of the insured at the time disability commenced or his average monthly earnings for the period of two years immediately preceding a disability for which claim is made, whichever is the greater, the insurer will be liable only for such proportionate amount of such benefits under this policy as the amount of such monthly earnings or such average monthly earnings of the insured bears to the total amount of monthly benefits for the same loss under all such coverage upon the insured at the time such disability commences and for the return of such part of the premiums paid during such two years as shall exceed the pro rata amount of the premiums for the benefits actually paid hereunder; but this shall not operate to reduce the total monthly amount of benefits payable under all such coverage upon the insured below the sum of $200.00 or the sum of the monthly benefits specified in such coverages, whichever is the lesser, nor shall it operate to reduce benefits other than those payable for loss of time."
(b) The foregoing policy provision may be inserted only in a policy which the insured has the right to continue in force subject to its terms by the timely payment of premiums:
(1) Until at least age 50; or
(2) In the case of a policy issued after age 44, for at least five years from its date of issue.
The insurer may, at its option, include in this provision a definition of "valid loss of time coverage," approved as to form by the commissioner, which definition shall be limited in subject matter to coverage provided by governmental agencies or by organizations subject to regulation by insurance law or by insurance authorities of this, or any other, state of the United States or any province of Canada, or to any other coverage the inclusion of which may be approved by the commissioner or any combination of such coverages. In the absence of such definition, such term shall not include any coverage provided for such insured pursuant to any compulsory benefit statute including any workmen's compensation or employer's liability statute, or benefits provided by union welfare plans or by employer or employee benefit organizations.