The current New Yorker has a remarkable feature about the classical pianist Joyce Hatto, who died last year. She'd made some recordings in the 60s that had passed unnoticed but then in the last years of her life she began to be much-celebrated among the fanatics who inhabit the classical music communities on the web. She could not perform in public because of her health but many Hatto recordings were issued on a small label owned by her husband. These had glowing reviews in legitimate publications like The Gramophone. When she died in July of last year The Guardian's obituary described her as "one of the greatest pianists Britain has ever produced".
However there were some who wondered how such a distinguished performer could have remained unknown so long. It was only when a fan put one of her CDs into his computer and it was interrogated by the Gracenote database that it was revealed to be somebody else's work, as were all the rest. (Gracenote identifies particular CDs by reading the length of the tracks.) Her husband still insists that the scores of CDs he issued were largely his late wife's work and that he had merely inserted extracts from other recordings to cover passages where she made involuntary noises because of her illness. If you can't be bothered to read the whole thing you can listen to the writer Mark Singer talking about it here.
You wonder whether other areas of music could be susceptible to a similar con. Many years ago somebody sent tapes of established acts like Steely Dan to the a & r departments of various record companies and then published the inevitable rejection letters, but that probably meant that they didn't even listen to them. Presumably only in the world of the classical repertoire could such an elaborate deception succeed, at least for a while.