A. The territorial jurisdiction of the several justice of the peace courts within the parish of East Baton Rouge, as they exist on the effective date of this Section, shall continue and shall not be diminished or otherwise changed by reason of the annexation into any municipality within the parish of all or any part of the area comprising such territorial jurisdiction of a justice of the peace court.
B. Whenever, by reason of annexation, the territorial jurisdiction of a mayor's court or a city court is extended into all or any part of the territorial jurisdiction of a justice of the peace court theretofore existing, the territorial jurisdiction of the mayor's court or the city court, as the case may be, shall be concurrent with that of the justice of the peace court.