The "district" in reference, was dissolved or it ceased to exist and to identify itself as a district, after it was conquered by the Arabs. After the loss of the district, the sub-districts went under the legislation and control of the second district in reference, Arż Bābel (I'm not sure if that's the name of a district or the name of the leader of a particular district, but I'm sure you do).
But after ʿAlī b. Abī Ṭāleb came into power, the district of Arż Bābel lost the sub-districts of the lost district, from which it acquired them in the first place. The district that was lost after the Arab conquest was reconstituted after ʿAlī b. Abī Ṭāleb rise in power (Assuming that 'ʿAlī b. Abī Ṭāleb' is the name of a person).
PS: Sorry that I'm not certain with the names. But I believe the meaning is roughly what I have explained here.