answer:Expiration dates are a guideline. They’re basically intended to say “ok, if someone with only basic common sense is completely lax about taking care of their stuff, how long should this last?” That’s why the expiration date on meat is yesterday, and why cereal can “last” for years. In that situation, I’d probably ditch the old juice, just as a precaution and keep the unopened juice. If the expiration date on the unopened juice was several years ago, it’d be an issue, but a few months isn’t anything to worry about.