I think that it all comes down to two observations:<br><br>1) We aim at a good precision; recall is irrelevant. <br>In other terms, we must never present an unfree work as being Free, but missing some Free work is of no consequences.<br>
<br>2) 100 years might be a very long time compared to Human lifespan, but it is not compared to typical periods related to copyright.<br><br><br>This being given, it becomes logical to start from a 150 or 170 years figure.<br>
&nbsp; -- Rama<br>