I’m not much of a believer in “use by” dates. Use your common sense. I’ve had milk that was a week past its date and was still good. On the other hand, I’ve had milk that still had a few days left and it was soured. In the case of fresh foods, use your nose. If it smells good, it’s likely good. In the case of instant mashed potatoes, unless they get bugs or something, I would think they could survive a nuclear holocaust and still be good. Glad to hear you used them and all is good.