NEW YORK - Over the last three years, many of the rules that seemed to govern the Kentucky Derby have crumbled faster than Tokyo under Godzilla's wrath.\nIn 2006, Barbaro became the first horse in 50 years to win the Derby off a layoff of five weeks or more, posting the largest winning margin (6 1/2 lengths) in 60 years. In 2007, Street Sense became the first in 24 years to win off only two prep races at 3, the first 2-year-old champion in 28 years to win, and the first Breeders' Cup Juvenile winner to win in the Cup's 23-year history. And last year, Big Brown became the first in 93 years to win the Derby in only his or her fourth career start and the first in 79 years to win from post 20.\nMany of the old Derby rules were grounded in such time-tested assets as fitness and seasoning. These are still important assets, but they don't seem to be as all-important as they once were. The same is true with pedigree. A stout pedigree used to be a major requirement. In recent years, however, not so much. Such horses as Big Brown and Smarty Jones (in 2004) won the Derby with miler's pedigrees.\nThose of us who weren't quick adapting to these changes have managed to come around. For example, yours truly was against Barbaro and skeptical of Street Sense but had no reservations about Big Brown. Recognizing just what role the Derby rules play, if any, is important because new historical factors are threatening to come into play.\nThis year, we might see Stardom Bound attempt to become the first filly in 21 years and only the fourth filly ever to win the Derby. We might see the most serious threat yet by a colt trying to be the first to win the Derby after prepping in Dubai. Among the candidates are the reigning 2-year-old champion, Midshipman; the hot Desert Party; and Vineyard Haven, should he recapture his best form.\nAnd we might see a strong challenge to the granddaddy of all Derby rules. The last Derby winner who did not race at 2 was Apollo in 1882. That's 1882, as in 127 years ago.\nBut anyone who saw Dunkirk win last Thursday at Gulfstream Park probably can't help but wonder if this Derby rule might not be the next one to fall.\nDunkirk was awesome. That he ran away from a loaded allowance field by almost five lengths going 1 1/8 miles and earned a 98 Beyer Speed Figure only begins to tell the story. Dunkirk was caught ridiculously wide on the first turn and was only a little less wide the rest of the way. He lost so much ground it looked like he ran a sixteenth of a mile farther than anyone else.\nBut Dunkirk did not race at 2. In fact, he did not debut until Jan. 24, when he was a stylish winner. So questions arise. Is Jan. 1 really a firm cut-off date, or is it largely arbitrary because it coincides with the Thoroughbred birthday? Who are the Derby winners since Apollo with the latest racing debuts? When did Apollo make his racing debut?\nUnfortunately, getting answers is difficult. For source material, I had to settle on a copy of past performances of all Kentucky Derby entrants from 1955 through 2000 that I received from the National Turf Writers Association in 2001. After reviewing those past performances, here are some partial answers:\nOf the last 54 Kentucky Derby winners, the ones with the latest racing debuts were Fusaichi Pegasus (2000 Derby winner), who debuted on Dec. 11; Majestic Prince (1969), who debuted on Nov. 28; and Smarty Jones (2004), who made his first career start on Nov. 9. Sunday Silence, the 1989 Derby winner, is next in line with an Oct. 30 debut.\nIt's interesting that two of the top three were from 2000 on, which is emblematic of the evolving philosophy among trainers of good horses that infrequent racing is better, and I suppose Dunkirk fans can take this as a sign of hope. On the other hand, it was surprising that only three of the last 54 Derby winners made their first starts after October and that there is a 44-day gap between Fusaichi Pegasus's debut and Dunkirk's. That is substantial, and not encouraging if you're a Dunkirk fan.\nBut as we have learned, what used to be critical factors in identifying Derby winners aren't as important anymore. I have a theory on that. Back when the Derby rules mattered, there was a greater depth of quality in Kentucky Derby fields, so rules that put an emphasis on factors like fitness and seasoning were helpful in distinguishing between horses of comparable ability. These days, there isn't as much depth of quality in Derby fields, so the premium has shifted to talent, as in, how many can really run? And in that regard, Dunkirk does not fall short.