The rulebook states "If there are no more Resource tokens to put into the Stock, mix in those that were put to one side".
What is this "one side" place? From what I understand when you sell or fulfill contracts, the goods you used get placed into the box to be mixed with all the other Resources again. Then at the end of the round you refill from that?
Or do you keep the ones you sold to the side and refill with whatever is in the box until you run out and then shuffle the discard back to replenish the stock?