トリビア Because the war in Europe made it so difficult to track down who had the rights to most operas (coupled with the studios reluctance to pay the required royalties) all the operas performed in the film were either in the public domain (i.e., no-one owned the rights to them) or were based on classical music that was in the public domain.
The film makers were able to slip in a reference to the opera Faust (which featured heavily in the original novel) by having Christine appear in the Marguerite costume as she comes off stage at the end of the film.