I have recently read a book about the world cup where all the races of its history were accounted for and for Paris-Tours and Lombardia it was always the same story with the leading riders only having eyes upon each other.
It even looked like Zabel deliberately tanked Paris-Roubaix one year in the sense that he didn't want his group to ride too fast because he then risked dropping and losing an opportunity to score points even if that meant he couldn't win the race.
From memory and some CN archive search
at least for Lombardia
2004 - both Bettini and Rebellin dropped well before the finale
2003 - Bettini won the WC before Lombardia
2002 - i think Bettini had won the WC before
2001 - Dekker won the WC before
2000 - i think the same for Zabel
I guess the closest thing was 1999 and I suppose 1997 when Bartoli IIRC was just happy to finish 4th and did not contest the finish
Edit: IIRC in the last few Paris-Tours WC editions not much happened from WC contenders behind the breaks