Not even lords and dukes have that data, why would I assume the bankers will?
Because the current data available to lords and dukes doesn't consider seasons... among a number of other things.
At one point, I did write a page that included food data that attempted to take seasons into account. It kept having all kinds of problems. However, this was back when there were variable harvests, which confused the calculations significantly.
I could probably write one now that would properly take seasons into account, with daily harvests.
There's never been a conscious effort to keep accurate medium-to-long-term food production data (ignoring weather, which is unpredictable) out of Lords' hands; it's just not been a trivial proposition.
