Gavra, there’s a famous Chazon Ish about this. He talks about 2000 year tekufos. I don’t have the citation on hand.
Simply put, the twelve month lifespan (which is itself a machlokes) is how the identity of treifos is determined, but once we have a list of which perforations are considered a treifah, it’s still a treifah even if it lives longer, including if new treatments become available. The gemara you cited clls it a siman, not a sibah.
ZD, basically correct, but soft cheese is actually a machlokes, although common minhag (and OU policy) is to be meikil.