What happens when there are injuries or defects in the lung can be benign when it's in the kidney. But when it's fine in the lung, does that mean it's automatically find in the kidney? But really, each kind of ailment or injury is specific to that same organ, because there's no guarantee that it won't be a problem in a different one. Also, the case of a "shriveled lung" - at the hands of heaven, and not as a result of an animal's attack, per se. Maybe it shrunk in fear... Well, in that case, the animal would either be kosher or a treyfa, depending on how the text is to be read. Plus, a method of figuring out whether the lung can be expanded, which tells you that the animal would have recovered from the shriveled lung(s). And if they don't, then the indication is that the animal was treyfa.