We list food production in the statistics, twice even, total and supply.
Production, yes; storage, not at all. A realm could have massive production, yet constantly sell the food; another realm could have a very small surplus, but horde it forever and buy food from their neighbors and have a massive stockpile. Aurvandil, Morek, and Iashalur all have stockpiles, but there's no way for my character can find that out.
