Other mistake: The first time we see George Loomis back at the Rainbow Cabins after his supposed death he's by the garbage cans in the back of cabin B with a brick wall on the left. The next time we see him two shots later the film has been reversed with the brick wall now being on the right. (00:46:45)
Other mistake: When the invitation to the Hunt Ball is shown on the screen, it says that the ball is on Thursday, March 7, but on the night of the ball when Lena gets the telegram from Johnnie, the date of the telegram is March 8, 1938, which would have been the next day. And March 8, 1938, was actually a Tuesday and March 7, 1938 (the day of the Thursday Ball), was actually a Monday.
Other mistake: Near the end, Harry Lime is trying to escape through the sewers of Vienna. There is an opening to the street; Harry puts all his fingers through the holes, trying to lift the metal plate, but Harry has a pistol in his right hand; there is no way he can poke all his fingers through with his right hand with the pistol in it.