It certainly doe's matter where they come from and how well bred and close to type they are. Hatchery DC's will breed fine because they aren't real Cornish, WLR's & Darks do breed better than the whites if they are of good quality and must be bred while young to improve your chances. Cornish unlike other breeds will come in and out of fertility cycles so you have to be on the lookout for this and when they season up. Most common folks confuse the Cornish X very often with the standard cornish, so that is where the breeding questions come in.