Canned Olives will last a long time as long as the can of olive has never been opened.
Olives that remain sealed in the can are good for at least 10 years and longer as long as the can does not have swelling, bulging or any rust or holes in the olive can.
If the can of olives is swelling, bulging or has holes or rust then the canned olives are likely bad and should be thrown out.
Although the canned olives have an expiration date on them it does not mean the canned olives are actually bad.
Instead the expiration date on the canned olives just means the canned olives are not as fresh as they were before the expiration date.
Canned olives can keep good in the sealed can for many years past the expiration date.
Once you open the can of olives though the opened canned olives should be eaten within a week or less and they should be kept refrigerated when not eating them.
The olives are best eaten within a few days of opening them and if you see any mold or they smell bad then throw the olives out.