I've used paint that was almost a decade old and it matched (store the
can upside-down, a painter once told me- it works). With a ceiling I'd
expect it would match closely enough that nobody would notice,
especially with all the glare and shadows on a ceiling (look up right
now- does your ceiling look all one color?).

Don't agonize over this- try painting that area, and if you don't like
it you can finish painting the rest of the ceiling.

But look up first right now where you're sitting.