I can only go from my own experiences and I have not had a problem with recall with the Cockers that I have owned from puppies.I introduced the whistle from an early state,first getting them to sit with the open palm signal and then a blast on the whistle(this comes into it's own later when teaching them to stop/sit at a distance). You can also start using the recall whistle whilst they are still young,start in the garden with multiple pips until they come right back to you.You must give the right body signals to encourage your pup to return to you,get down to it's level and smile!, give it a fuss and a "good dog", this should be all the reward it needs.When you let your dog off lead don't allow it to just run off,make it sit and and only go when you release it with a voice or hand signal.If you start at an early stage you should get good recall, get a good bond with your dog and it will want to be with you.
I may sound pompous in this but it is my experience and I am having the same results with Bailey who I had as a rescue dog last
November.I am not hard on my dogs (I am classed as "soft" by the local shooting/Gundog fraternity) everything they have done for me has been done out of love.