Ray Saintonge wrote:
At some point we need to be able to say to our users:
"We have a high
degree of confidence that this [specific] material is free, but these
difficulties exist: ... Use it at your own risk."
There is this idea of having copyright insurance. There are useful works
published long ago and never republished, whose authors' whereabouts are
completely unknown. Digitize them and publish them on the Internet, but
insure them, so that if heirs ever appear a reasonable royalty may be
paid to them.