Only Dwilight and the Far East have seasons.
As has been stated, Bankers cannot control any food movements, they can only organize and direct the Lords in doing so. This means that if you have set up no caravan offers, and no automatic transfers, and have not sent out any caravans yourself, your food is just sitting in your region rotting.
Bankers should not have any more information about an individual region's food status than the Lord has himself; however, they have broader information about the entire realm. Similarly, Dukes have information about the food status of their Duchies.
