There is a thing called gift card breakage. It’s been about 10 years since I worked for a company that did this, but… the deal is you figure out how many gift cards are redeemed after a certain age, like 5 years. If that is 50%, you can claim 50% of your outstanding value of gift cards older than 5 years as profit.
It’s just a statistical model; the gift cards are still valid and can still be redeemed. It’s just, when you have a large enough pile, you can statistically predict fairly accurately how much won’t ever be redeemed.
It is very similar to the breakage companies take on accounts payable. They know as an account gets older and older, the likelihood of it getting paid goes down. So they know an invoice unpaid after say, a year, has a certain percentage change of never being paid, so they try to bundle it up and sell it to someone else for more than they would be able to collect on the bundle, less expenses. Those bundle buyers (debt collectors) try to buy it for less than they will collect. Fun games all around.