when making the top tier or second some of the materials are the same so when you use them for the top tier you would then have less over all resources to use at a lower tier as well. the purple resources are used in the middle and the top tier. The number it shows is the total amount of that tier you could create if you used all your materials there. the top tier uses twice the amount of the purple resource when crafting so for every top tier you forge the middle number should go down by two. hope this helps.