Anyone who dips into research on the Third Line of the mobilization of 1815 needs to become familiar with the boundries & numbering of the Military Divisions. They had commanders and were more or less important in moblization and defensive arrangements. If I am not mistaken, the initial control of National Guard units vested in the Military Divisions where they were formed.

Meanwhile the aggregration of NG units under NG commanders independent of the MDs or assignment of NG units to First Line units went on apace.

It's a whole level of interest and research.