Do you have information about which Reserve regiments existed? It seems there were at least two, Hermann Cron (Geschichte des Deutschen Heeres im Weltkriege) mentions Res.Jäg. z.Pf. 1 and here is a tag from the second (not mine, linked from here):
There was only one the: Reserve-Jäger-Regiment zu Pferde Nr.1
The tag above is from the Ersatzeskadron of the Jäger-Regiment zu Pferde Nr.2
Every Kavallerie-Regiment had 5 Eskadrons in peacetime and in wartime 4 where Feldeskadrons and one became Ersatzeskadron and stayed in the homegarrison.