Good point. I actually wasn't trying to argue that the skills were going to be totally forgotten (though now I'm thinking maybe I kind of implied that), and certainly not irrecoverably, but just that they were going to be *largely* forgotten. What I was really trying to do was think about what things change fast and what things change slowly. Fashion changes fast, for instance. Clothing technology changes somewhat more slowly, but still pretty fast. But certain traditions change really slowly.

Not that there can't be exceptions, and not that a story needs to hew to that observation, necessarily. Just that it's worth noting that some things seem, generally, more change resistant than others.