I think you are right, I don't have a subscription to the Shanghai Metal exchange (and thought it was around 20-25US/WMT) but some did post a screen shot and said it was a recent data and it was around 40US/WMT but looking at this article nickel price definitely hasn't doubled since 2015 so their margin is actually way less than I thought, hence it explains the <3 years (now it makes more sense.....)