Cattle (and all market animals) lay on fat from the front of their body toward the back, meaning they deposit fat over the rib first, and as they get heavier...fatter...more "finished" they lay on more fat over the other parts of the body. When you see one with fat pones on either side of the tail head, you know they're fat because that's obviously at the back of the animal.
Same is true with the cod. When a steer is finished, he should have some fat in the cod. A "greener" or underfinished steer will have wrinkles in the skin...on a real fat steer, the cod will be full of fat and the bag will appear smooth and full.