The board shall determine the amounts necessary to be raised by taxation during the fiscal year and shall fix the rate or rates of tax to be levied which will raise the amounts of money required by the district. These acts by the board are a valid assessment of the property and a valid levy of the taxes so fixed. The amount of this levy shall not exceed the amounts permitted by any maximum property tax rate limitation in the Revenue and Taxation Code, provided, however, that if no tax was levied by the district for either the 1971–1972 of the 1972–1973 fiscal year, and the district incurred expenses in such years, which expenses were paid from revenues other than taxes, then the maximum levy shall not exceed fifty cents ($0.50) per one hundred dollars ($100) of assessed valuation per year.