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Lisanne is a trusted home cook.
Confectioners or powdered sugar is pretty shelf-stable. It's just sugar and cornstarch. I use a box over a period of years. I'd have no qualms using it past expiration date.
Nancy is a trusted home cook.
FYI safety also confirmed by stilltasty.com site which uses cdc, fda & usda data.
They say it "keeps indefinitely"
Little chance of spoilage, but it can absorb odors in storage.