Original: The result was often a merger of the two into a "district" (eg Rotorua) or a change of name to "district' (eg Waimairi) or "city" (eg Manukau).
Simplified: Because of this, sometimes they put the two together, making a "district" (eg Rotorua). Or sometimes they changed the name to "district" (eg Waimairi) or "city" (eg Manukau).