> what if one encoutered a collector who had a sole surviving copy
> of a performance by a major performing organization...the
> person does not own the rights to the performance recording

No, but the recording itself might have value if sold to someone who could
release it on CD. I assume that in Europe, after 50 years, the US copyright
issues would not apply, so you might be limited to selling it to someone in
another country. What you would get for it is another matter. If, like so
many classical CDs, they print a run of 1000 and that's all, the  value
would be limited by the potential market.

js