Where in any school district maintaining grades 1 through 8 or grades 9 through 12, at any time after July 15, 1965, and prior to the effective date of this Act, a majority of the legal voters voting on a proposition to increase the maximum annual educational tax rate of such district to a rate in excess of 1.60%, but not in excess of 1.81% upon the value, as equalized or assessed by the Department of Revenue, have voted in favor of increasing such educational tax rate, and the election was otherwise held in substantial compliance with the law then applicable to such elections, such election is declared to be legal and valid for all purposes, notwithstanding that at the time of such election the maximum annual tax rate applicable to such school district was 1.60% of the full, fair cash value as equalized or assessed by the Department of Revenue upon the taxable property within such school district.