This is a side post to something flashmax said abut his mother working at the school pantry. I did too. In about '69 and '70, there was a government program where poor kids could get a part time job in the storerooms putting away truckloads of canned and powdered goods and keeping the stock rotated. They paid you by giving you pretty much unlimited food in the cafeteria. There was another program where you could get free lunches, but some of us were proud enough to work rather than get a free tray of food.
Probably 1/2 of all the cans were marked USDA. There was a date code read by the rings pattern on the #10 cans. It was amazing, most of the canned beef was from central American countries and was 5-8 years old when we got them. Most of the peanut butter was over 10 years old, veggies and fruits were 3 or 4 years old. We all ate that food, and didn't get sick.