A series of bonds or notes may have any number of interest rates or yields, subject to any limitation on such number fixed by the governing body of the issuing local government unit, but, unless further limited by the issuing local government unit in the official notice of sale, no yield for any stated maturity date in the last two-thirds of the period of the series may be less than that stated for the immediately preceding year which falls within the last two-thirds period.
53 Pa.C.S. § 8144