I don't have your answer, but would think it has a lot to do with the core material. Wood can be resilient , particularly when glued (like most wood cores). Carbon fiber isn't going to ever change. Some other synthetic cores won't change much, either. I still have an old pair of Stockli Spirit Pros that I used when my kids started skiing, and recently skied a day with them. They still feel "new" and have a synthetic core with titinal (aluminum).
I collect and play with hickory golf clubs and occasionally need to replace a shaft. I always look for an older good shaft before a new one for several reasons...and these shafts were all made before 1928! The old wood was prone to warpage if not stored flat, but that should not happen in a ski because of the way the strips of wood are glued together, and the type of wood used.