Garry
I was curious how the flank protection battalions were selected and wondered if seniority/brigade order would help explain it.
According to seniority the infantry of the Reserve Division would have marched with the Guards Brigade leading followed by the 3rd Brigade. The brigade order, in line of battle, of the Guards brigade was [and still is] the 1st Guards as the right hand [senior] battalion and the 2nd as the left hand battalion [with the 3rd Guards in the middle – not sure about the composite Grenadier and Light company units].
The brigade order, in line of battle, of the 3rd Brigade would have been 12th on the right, then the 42nd then the 44th finally with the 33rd on the left.
Each brigade was clearly ordered to provide a battalion as a flank guard, so the Guards sent their left hand battalion [2nd Guards] to protect the left flank at Erp and the 3rd Brigade their right hand battalion [12th Foot] to protect the right flank at St Michelsgestel.
So that seems to work out.
Paul