One tell-tale sign is the bird's need for feed. The Jumbo CornishX are pigs. They can't deal with hunger.
Our county 4H leader was telling us that without the high protein feed, they JCX's will start to "fail" by week 6. In other words, they need to big protein food for their big growth rate. They can free range easily, but it's a supplement----given the choice, the fatty will sleep in the food bin. He can't run/jump/roost, so he is easy prey. And by week 10, they're usually so fat that organ failure starts...so be prepared to transfer him to the freezer between weeks 6-9. If you can't do it, no judgement---but you might find a predatory bird sanctuary or large animal rescue that might take him.
-Good Luck!
-Aim
