Towards the climax of the film, when Mata Hari confronts General Shubin, she is wearing a ring on her left ring finger. She hurries out of the room, and moments later she encounters Rosanoff. He takes her by the hand, and the ring is no longer there.
Near the beginning of the movie, Lt. Rosanoff flies over the German lines to land in Paris. The movie is set in 1917. The plane Rosanoff is flying using a Pratt & Whitney R-1340 Wasp engine which was ubiquitous in aviation from the 1930's through the late 1940's. However the engine was not built until 1925.