The people who sell food have told me that they are extremely generous with the use by dates.
I think if it were me I'd open it and see what I thought. If it's really large though, it might take a while to get through.
How could anyone here on this site possibly know for sure? If it were me, I would use at least the same caution (if not more) with my cat that I use for myself - which is pretty much 'when in doubt, throw it out'.
You can always ask some of the local rescue centers what their view is and if they say they would take it since it is unopened, then donate it to them.
Is it worth the cost of a bag of cat food to dwell on it very long?
The problem is that dry food doesn't last, even unopened, very long. At the least, it gets a funky odor and that can be off putting. Unless you had it in a freezer all this time it's likely not edible and could be unsafe .