A cursory look back at previous Preakness winners in the modern age results in the following. Please excuse any I got wrong.
Those which didn't run in the Derby
2017 Cloud Computing
2009 Rachel Alexandra
2000 Red Bullet
1983 Disputed Testimony
I took a look back because I read somewhere that 80% of the Preakness winners came from the Kentucky Derby fields in some recent period of time (? this century).