Strike the Gold (1991) was the last Blue Grass winner to go on and repeat in the Kentucky Derby. None of the next fifteen dirt or six Polytrack winners went on to Derby success.
Two Derby winners came out of those final fifteen Blue Grass Stakes run on dirt. Sea Hero (1993) and Thunder Gulch (1995) finished out of the money at Keeneland, perhaps victimized by the speed bias, before going on to Derby glory.
Polytrack runnings of the Blue Grass have been similar. Street Sense was narrowly-beaten in that 2007 Blue Grass, then went on to dominate the Kentucky Derby. Since then the Derby winner has come from other venues and Blue Grass graduates have not been a factor.
Matt Gardner, looking at Blue Grass results in the Polytrack era, found that “the top 3 finishers in the Blue Grass are 13-1-0-2 in the Derby since 2007.”
Compare that to the Santa Anita Derby over the same years: The top three Santa Anita Derby finishers are 13-1-1-0 since 2007. Or the Florida Derby: 9-1-1-0. If there’s an irrelevant Kentucky Derby prep lately, it’s the Wood: The top three finishers out of Aqueduct are 10-0-0-0 since 2007.