Except as provided in this section no person shall hereafter be elected or appointed to office as county superintendent of schools of any county who does not possess a valid credential issued by the State Board of Education of the type designated in Sections 1205 to 1212, inclusive, for each class.
Where a county changes from one class to another because of an increase in the average daily attendance in the public schools of such county, the incumbent county superintendent of schools in that county shall not be prohibited from continuing in office and shall be eligible for reelection to the same office regardless of whether he possesses a valid credential otherwise required in a county of that class.