Experience is a tricky thing. As much as we like to make rules about what horses can or cannot do based on their experience the truth of the matter is that a horse need not experience something fully in order to excel at it. We see that all the time with first time starters that blow their rivals off the track.
The big "rule" that people are pondering this year is the "curse of Apollo". Going all the way back to 1882 no horse has won the Derby without racing as a 2yo. Many horses have tried including 10 in the last decade. Curlin managed the best of the recent competitors with a non-threatening third but with the way the modern thoroughbred is trained do we really think it matters if a horse ran last August? Does that really help their Derby chances?
If a trainer can't get enough fitness and the proper experiences into his horse during the spring then the horse likely shouldn't be running.
So does any experience matter? The experience I demand from my Derby selections is that they've faced large fields. The field size is one of the most difficult obstacles for Derby horses to overcome. No horse from 1996 to the present has won the Derby without first facing a field of at least 10. These horses weren't a bunch of longshots either. Horses like War Chant, Louis Quatorze, Halory Hunter, Curlin and Millennium Wind all succumbed to this factor. Many of them specifically had difficulty negotiating the traffic.
Another bit of experience I like to see is that horses have attempted stakes company at 9f. You might be surprised to learn that 17 horses have tried to win the Derby without a stakes prep at 9f. Only Eight Belles got anywhere close and even she didn't threaten the winner. I think going long at least once against good horses gets a horse battle ready.
If you combined these two experience factors and tossed every horse who violated them you'd have removed 50 Derby losers from contention. That's 21% of the total number of Derby starters. Not surprisingly many of the horses who failed to race as 2yo's also missed out on one of these experience factors but I feel much better banking on a statistic that has some merit instead of some old curse. One of these days an unraced 2yo will win the Derby. The first four months of the year is more than sufficient to get a horse ready as long as a trainer is getting the right kind of preps into a horse.