When Major Arnold is listening to the recording of Beethoven's Fifth Symphony, the record finishes the first movement and carries straight on to the second. Long playing albums, which ran at 33 1/3 rpm, were introduced in 1948, but the record shown is a 78 rpm one. The performance of the 5th Symphony would have been on a set of five 78 rpm records, one movement each, split over the two sides. It should not be possible for the second movement to start without the record being changed.
In one of the library scenes, the boom mic and the arm holding it are clearly visible.
When Emmi is buying records from the vendor she asks in German the price of the records. The vendor replies five hundred. He should have said "fünf," five in German. Since she is German, there is no reason for the English number.