Some possibly relevant trends:

In that last 56 Preakness runnings, horses that ran in the Derby accounted for slightly less than half of the entrants (49.1%), yet accounted for 82.1% of the wins and 76.8% of the exacta finishes. That means that horses that had not run in the Derby before the Preakness accounted for only 17.9% of the winners, yet were over 50% of the horses that entered. In terms of the exacta, these horses represented 23.2% of the exacta finishes. So approximately a little less than one-fourth of the time does a non Derby horse finish in the Preakness exacta – so basically, once every two years.

Winners of the Preakness since 2000 – Last Race:
Kentucky Derby – 15
Wood Memorial – 3
Kentucky Oaks – 1

Superfecta finishers in the Preakness since 2000 – Last Race:
Kentucky Derby – 50
Aqueduct – 9
Keeneland – 8
Churchill Downs (not Derby) – 4
Pimlico – 2
Oaklawn Park – 1
Santa Anita – 1
Hawthorne – 1