Originally Posted by JerrySTL

I know of a bike shop that had a cinder block hanging from a derailleur cable for over a month. There was no stretch after that time. It's more about the cables wearing into the gable guides and somewhat where the cable is squished by the pinch bolt on a derailleur or brake.

Also if you look at the ends of the cable that go into the shifter, often it has some slag or extra uneven metal that settles in at times. I've seen people take a small file to clean up such material.