Probably the greatest working cocker of all time was Field Trial Champion Speckle of Ardoon who won the Cocker Championship three times in the 1970s.
Speckle was out of an Elan (working pedigree) bitch, by a Tireragh (show pedigree) sire, that went back to the famous Sixshot show kennel.
Because working cockers don't have to match a standard or blueprint in the breed it doesn't matter how big or small they are, or whether they are "mismarked". The only criterion is that they are biddable, will hunt, and will retrieve, and that they are registered as cockers at the Kennel Club. Some people think that there have been some sneaky springer spaniel genes clandestinely imported into the breed in the last twenty years. This may have led to an increase in size in some working cockers, but there are also small cockers working which look more like show cockers. You pays your money ..........
John