Canned gravy does eventually go bad but it takes around 5 years or longer for the canned gravy to actually go bad enough to where it's no longer safe to eat.
The gravy being sealed in a can makes it last longer than it would when out of the can.
I've heard that canned gravy is no longer good 2 years after the expiration date on the can but I've actually had some canned gravy that was in a house I bought and the canned gravy was 10 years old.
I thought it was gonna be bad and was gonna open it up and see and the canned gravy was still good and safe to eat.
So you can keep canned gravy for a long time before it goes bad.
After 10 years it may not be any good but I've never kept any canned gravy or any canned foods that long.
Canned gravy is good well past the expiration date so there's no need to throw the canned gravy out or any other canned foods past the expiration date.