The provisions of 1975 Iowa Acts, ch. 199, are retroactive in application to all joint agreements entered into and executed prior to July 1, 1975, under this chapter, on behalf of cities which, on the date of executing the agreements, operated existing electric generating or distribution facilities. However, all such joint agreements which complied with the provisions of this chapter prior to amendment by 1975 Iowa Acts, ch. 199, are also in full force and effect according to their terms, and are not rendered invalid in any respect by any provision of 1975 Iowa Acts, ch. 199.