Here's a weird one I learned in the 70's when playing with uber-expensive molded PVDF for laboratory apparatus. Fluorocarbons, although damned inert, can have a stressed state from tooling or molding. This stress will be self-healing over perhaps a long time (a year+), or released with thermal treatment. The costly evidence was when newly assembled Pipetman developed innocuous tiny stress cracks along their body faces after many months in service. The solution was simply to thermally treat (a standard autoclave cycle by the end user) again to stabilize the fluorocarbon mechanically.
When I decided to be disruptive and provide inexpensive Teflon-sheather power cables, boxes, and PCKits to A'goners many years ago, I thermally treated the raw Teflon-sheather cable to fully "cook" them so there would be no perceived break-in period. No user (there were a few hundred of you) ever claimed they changed with time. Hence I believe it's not the conductor metals that require, or can change with time marching on, but only the dielectrics used in or near contact with the conductors. So your "old" cables may indeed be especially nice!