Post Grape-Nuts Non GMO Breakfast Cereal, 29 Ounce (Pack of 10)

Q: Does anybody know the shelf-life of Grape Nuts?

Not sure what you mean by "shelf-life". I bought this on Amazon in February and the boxes that arrived show a "use by" date of January 2020, so i assume the suppler is drawing from relatively current stock.

Q: Anybody know where the 5g of sugar is coming from? It’s not a listed ingredient.

The 5g of sugar is what is inherent in the ingredients listed, as all carbs have natural sugars. When there is sugar itself added, it will be in the nutrient list as "added sugars." There are no added sugars in Grape-Nuts.