The official name of each educational service unit shall be Educational Service Unit No. ... of the State of Nebraska, and the individual number of each unit shall be determined by the State Board of Education. For educational service units existing on January 1, 1998, the number of the unit shall remain the same. For educational service units created by merger, the number of the unit shall be the number of one of the educational service units dissolving into the new educational service unit. For all other newly created educational service units, the number shall be any number not otherwise assigned to an existing educational service unit.