(a) Notwithstanding any other provision of this chapter, a member who elects to purchase retirement service credit under Section 31486.3, 31486.35, 31499.3, 31499.13, 31641.1, 31641.5, 31641.55, 31646, 31652, or 31658, or under the regulations adopted by the board pursuant to Section 31643 or 31644 shall complete that purchase within 120 days after the effective date of his or her retirement.
(b) This section is not operative in any county until the board of supervisors, by resolution, makes this section applicable in the county.