Unterelsaß different from Lower Alsace
Annexed municipalities from the neighbor department
The district of Unterelsaß corresponds exactly to the current département of Bas-Rhin, but not to the Alsatian territory before 1870. 
Under the terms of a particular agreement  that was signed in Berlin July 21, 1871, and in Paris July 31, 1871, 18 municipalities of the Vosges department were integrated into the new imperial district of Lower Alsace, subdistrict of Molsheim, canton of Schirmeck.
not same as not identical to distinct from separate from unlike