In the event of a late scratch before the first leg of the Pick Three, the bettor receives a refund. In the event of a late scratch after the running of the first leg, a consolation payoff is paid to bettors with winners in the other two legs.
https://www.nyra.com/belmont/racing/betting-faq
http://www.derbytrail.com/forums/showthread.php?t=64846