Mont. Code Ann. § 33-20-513

After July 1, 1979, any company may file with the commissioner a written notice of its election to comply with the provisions of this section after a specified date before July 1, 1981. After the filing of such notice, then upon such specified date, which shall be the operative date of this section for such company, this section shall become operative with respect to annuity contracts thereafter issued by such company. If a company makes no such election, the operative date of this section for such company shall be July 1, 1981.