I checked my literature ("Handbuch der Verbände und Truppen des deutschen Heeres 1914-1918", Jürgen Kraus) and that doesn't seem to be the case, locations of the Ersatz Bataillone as per Clovis' reply above.
According to "Führer durch Heer und Flotte", Friedag, 1914, A.K. XXI did not have its...