I could be wrong, but maybe there is a possibility that your great grandfather would have traveled to many different places as a cavalry officer and perhaps didn't have a concrete location as to where he served.
My 2x great grandfather was supposedly in the German cavalry during the 1890's. He was born in north western Germany, but family stories tell that he went through the Black Forest which is all the way in the south west.
But for all I know he could have been stationed there. Just a guess.