Lovely! Most Dunkelblau Infanterie Waffenrock are very plain, and most look the same. Red collar, red cuffs. But what makes this Waffenrock to 9. Lothringisches Infanterie-Regt. Nr.173 (Avold, III Bn Metz) XVI Armee Korps is those Brandenburg cuffs with the white vertical panel piped in yellow. It really makes this Waffenrock far more interesting.
M91 chinscales were not authorized for soldiers of this Regt. so unless this set came directly from the family, they have probably been added. Still a very nice Pickelhaube though and it makes a striking set.