A nonprofit hospital corporation which substantially indemnified subscribers and enrollees and was operating in 1965 under Chapter 11A (commencing with Section 11490) of Part 2 of Division 2 of the Insurance Code and which is regulated under the Knox-Keene Health Care Service Plan Act shall enjoy the privileges under the act which would have been available to it had it been registered under the Knox-Mills Health Plan Act and applied for a license under the Knox-Keene Health Care Service Plan Act in 1976.