800 bushels still isn't enough. Libidizedd needs over 1300 to make it through winter. Other cities require significantly more. I think your calculations are incomplete. You are counting on food coming in to the city every day, I think. But you're not accounting for the fact that the food coming in to the city has also been subject to rot for the entire time it was sitting in the warehouses of whatever region it was in. You have that food just appearing fresh every day.