Any member of the Legislature who is elected to office after the effective date of this amendment shall be eligible to serve no more than 12 years in the Oklahoma State Legislature. Years in Legislative office need not be consecutive and years of service in both the Senate and the House of Representatives shall be added together and included in determining the total number of Legislative years in office. The years served by any member elected or appointed to serve less than a full Legislative term to fill a vacancy in office shall not be included in the 12-year limitation set forth herein; but no member who has completed 12 years in office shall thereafter be eligible to serve a partial term. Any member who is serving a Legislative term in office or who has been elected or appointed to serve a term in office on the effective date hereof shall be entitled to complete his or her term and shall be eligible to serve an additional 12 years thereafter. This amendment shall be effective on the 1st day of the year following its adoption.