Not quite unsung but rare: Did any one hear or see the Amsterdam orchestra start to play the wrong piano concerto with Maria Joao Pires. It can easily be googled
An extraordinary event, to be sure, though thank goodness it occurred at rehearsal -- and not perhaps quite as extraordinary as Gershwin forgetting his own scores in concert (shortly before succumbing to a brain tumor). If Ms. Joao Pires left her music at home, that would be in Brazil these days, a bit of a trek from Amsterdam.
Here's a link:
http://blogs.telegraph.co.uk/news/damianthompson/100243153/pianist-maria-joao-pires-panics-as-she-realises-the-orchestra-has-started-the-wrong-concerto/ (http://blogs.telegraph.co.uk/news/damianthompson/100243153/pianist-maria-joao-pires-panics-as-she-realises-the-orchestra-has-started-the-wrong-concerto/)
Of course, it was a public rehearsal...