Tim Smith wrote:
I wonder how many open source projects provide a written
instrument signed by the copyright owner?
The GPL <http://www.fsf.org/licensing/licenses/gpl.html> says All
rights granted under this License are granted for the term of
copyright on the Program, and are irrevocable provided the stated
conditions are met.
A court would be presented with evidence that it is industry
practice to distribute under such licenses without signatures, and
given the statement of irrevocable grant, would find that the
nonexclusive license prevails.