Aidan O'Brien admits it can be hard to work out the pecking order of the Ballydoyle team after declaring seven horses for the Dubai Duty Free Irish Derby at the Curragh on Sunday.The handler has declared three of the six he ran at Epsom - Fame And Glory, Masterofthehorse and Golden Sword, while adding Byzantine, Drumbeat, Rockhampton and Hail Caesar to his formidable squad."With any of those big races you compete in, if you don't win it's always a bit of a disappointment but you can't win them all. The horses ran well and we're looking forward to the next day with them," he told RTE."Obviously there is not much between the horses that ran at Epsom and it's which ones come forward from there that is always a difficult thing to know."Some go back, some go forward and some stand still and usually at the races we find out. Sometimes you're surprised, sometimes you're disappointed and that's life."The Irish Derby is probably the most important three-year-old race over a mile and a half in Europe because all the good three-year-olds meet."If there are any question marks about Epsom, or France or anywhere else, it's always answered at the Curragh."It's a strong, even, fair track and you usually know who the best three-year-old over a mile and a half is after it."