Post by g***@gmail.comhttps://www.google.com/books/edition/Pierre_Monteux/7KmD9tU5Ht0C?hl=en&gbpv=1&dq=%22the+stereo+tapes+of+La+mer%22&pg=PA275&printsec=frontcover
Yes. His Boston Symphony La Mer was recorded using three tracks. They were mixed down to mono to produce the released recording. Part of the first movement (supposedly all that could be found), mixed to stereo, was released on the 1996 CD "The Age of Living Stereo" and on later CD issues. The stereo really transforms the experience, and if the whole of the session tapes could be found it would be a landmark reissue.