(a) The board by rule may adopt a system under which registrations expire on various dates during the year.
(b) For the year in which the registration expiration date is changed, registration fees payable after the 60th day and before the 30th day before January 1 of the next year shall be prorated on a monthly basis so that each person pays only that portion of the registration fee that is allocable to the number of months during which the registration is valid. On renewal of the registration on the new expiration date, the total registration renewal fee is payable.