Accumulated contributions other than contributions for prior service credited to or held as of June 21, 1971, as having been made by a contracting agency to the extent subject to Section 20506, with respect to miscellaneous members, and all contributions thereafter made by an employer pursuant to this chapter, other than contributions pursuant to Section 20806, with respect to those members shall be held for the benefit of all the members of this system who are now or hereafter credited with service rendered as employees of those employers, and for beneficiaries of this system who are now or hereafter entitled to receive benefits on account of that service.