If a vacancy occurs in any elective office, the Council shall, within thirty (30) days after such vacancy occurs, appoint by majority vote of the Council a person to fill such vacancy until the next regular city election, provided that if any such vacancy in the position of councilperson is not so filled by appointment within the said thirty (30) days, or if three (3) or more vacancies in the position of councilperson exist simultaneously, the City Clerk shall forthwith call a special election to be held within sixty (60) days thereafter to fill such vacancy or vacancies for the unexpired terms of the individuals whose offices have become vacant; provided, however, that no vacancy in the position of Councilperson shall be filled by special election as above provided if the term of office of the Councilperson whose office has become vacant expires within ninety (90) days after the vacancy occurs, notwithstanding the foregoing.