I don't seem able to update anything after the buy and sell prices i.e. demand and supply
Not sure I have the patience to play this game without the trade data.
Possibly you are not putting the level of the demand/supply in addition to the quantity? The data in those fields require a number and a letter eg: 467L (L means LOW). M = MED and H = HIGH. Otherwise you can just put a "?" if it is some amount but you don't bother with the exact number. The demand field can all be "?" - it doesn't really matter. The supply field I only update the exact quantity if it is below 1000, otherwise I just put a "?" there too when the commodity is buyable.