6000 Cr per ton is the figure in the Treasure ship adventure. Clans of the Aslan has the very best of Romer Dust Spice (A1) at 11,000 Cr per KG, and the worst (D?), from elsewhere, at 500 Cr per KG. Therefore it made sense to convert the 6000 Cr per ton from the adventure to 6000 Cr per KG. 6000 Cr per KG probably means that it is Romer Dust Spice, but not the very best. You could say that one of those 120 tons is the top A1 grade. That ton would make great presents for Aslan dignitaries or allies, or would be just what the "Alley Cat" is looking for to blackmail / poison Aslan nobility!