Can cables have a shelf life?

No....except maybe exposed ends...which can of course be cleaned. Also, if cable has been twisted, bent or abused, than maybe yes...

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!

subaruguru - Thanks for the post, very interesting. 👍

Mine didn't come with a use by date so I assume they're still good. 🤔

I’ve got them running. Thanks for the input. I have a loaner coming just to compare. It’s sounding better. I want to put the Kimber Hero back in then try something not Kimber. Going to insert an Audioquest Water in.

But I am certain night one was a bit messed up. The best time is right after the swap. A little brief background. I bought a Dynaudio Contour Ci center new to go with a special edition Dynaudio stereo monitor I also purchased with no matching center for a combined HT/stereo rig. I would not call the center dark as it’s not but maybe at first constricted may be a better word. I won’t go into a lot of adjectives but I was worried it may not workout. I let it run for a month. Doing some clean-up with cables. Adjustments etc and at some point the past week it was like a switch went on. Everything sounding fantastic. I mean I was really floored. I then remembered I had these cables and the amps are close now. They may reach and bet it will even go further. These were pretty awesome as I remembered from a decade ago. When I popped them in, that sound to me of constriction and voices sounding a bit dark back. Maybe worse.I couldn’t believe it and it was obvious. To be honest I expected nothing discernible. And I didn’t expect the much cheaper cable to sound better. Now for the hell of it I want to try a non Kimber.

It could well be the Water goes back and coin flip the other two.

But really thanks. This proved at least to me there may be some truth in run in. Wouldn’t think a used cable required anything. Sounding better now. Nothing like night one. Been running four days straight. It has really improved but I’d like to take my personal test further now.