(a) Except as provided in subsection (c) of this Code section, all annexation other than by local Act shall become effective for ad valorem tax purposes on December 31 of the year during which such annexation occurred and for all other purposes shall become effective on the first day of the month following the month during which the requirements of Article 2, 3, or 4 of this chapter, whichever is applicable, have been met.

(b) Except as provided in subsection (c) of this Code section, annexation by local Act shall become effective for ad valorem tax purposes on December 31 of the year in which such local Act is approved by the Governor or becomes law without such approval and for all other purposes shall become effective at the time such local Act becomes effective or such later date as provided in such local Act.

(c) Where an independent school system exists within the boundaries of a municipality, other effective dates may be established by the municipality solely for the purpose of determining school enrollment.