Provides that, in the event that any county has levied the tax authorized by this act and has, prior to June 26, 1975, pledged the tax revenues for payment of principal and interest on city revenue or general obligation bonds and has developed facilities for agricultural promotion prior to January 1, 2005, the county is exempt under this act in respect to revenue or general obligation bonds issued after April 1, 1991, only if the bonds mature before January 1, 2021.