The copper inside a cable's jacket is not expose to air and therefore cannot oxidize. It should be fine for a very long time. When you buy cable it does not need a "freshness date".
Only if you are using bare wire, the exposed ends as Garfish mentions can oxidize. The ends can be tinned with silver solder to stop the oxidation. Silver will oxidize, but is still a good conductor. Those ends can always be re-done every few years. You'll only lose an inch of cable each time.
If the cabes have copper spades connections, etc, they can be cleaned (as per Garfish).