I have been listening to the Furtwangler's Tristan und Isolde ( EMI Classics). I am quite impressed with the timber and range of Flagstad. The question I have is it really her. ? The story (so I have been lead to believe) is that Flagstad due to her maturity was unable to sing certain ranges i.e. the high C. Instead the person who sang in her place was said to be Schwarzkopf and as it was in a recording studio no one was the wiser for some time.( until someone disclosed the fact) Is there any true in this or is to merely idle gossip?