An unopened box of Tuna Helper can last for a year past it's expiration date and sometimes longer.
After the expiration date on the box of Tuna Helper it starts losing it's freshness but remains safe to eat well past it's expiration date.
So you can still use Tuna Helper that you have had stored for over a year and it will be good to eat and remain safe to eat.
But it's best to eat the Tuna Helper within a month or two of buying it and then buy more Tuna Helper.
I've had Tuna Helper stay in my pantry for a couple years and it was still okay to eat.
Once you cook the Tuna Helper and have leftover Tuna Helper it will remain safe in the refrigerator for up to 7 days.
You can freeze it in a freezer safe container and the Tuna Helper will last for a year or longer in the freezer.