
The test isn't whether GM knew--otherwise that would reward GM for its
stupidity.  The test is whether GM reasonably should have known of their
existence.  It works both ways--if GM had won the trial, and the plaintiff
turned up two witnesses who came forward after the first trial who should
have been located beforehand, too bad, so sad--no new trial.

Like Tim said, you don't get a new civil trial because you screwed up 
the first time around.  Unlike the criminal justice system, repose is
much more important in the civil justice system.