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This is an interesting question.
Deep frozen foods can keep for a long time, but that's usually measured in months, not decades! However, if you have access to cans over there, these could last a long time. Inspect the can carefully...if there is any bulging present, reject it. If the can looks great, open it and follow your senses. If it smells and tastes good, its probably ok. I would still do an experiment and eat very little of it your self. Wait a few hours perhaps to make sure you dont get sick. I would not eat any fresh frozen stuff like meat, etc thats decades old. If you are having too many doubts, drive to a nearest place to restock, even if it is 200 miles away. Essentially that's a very long day trip, but at least you get to be safe. Hope that helps.