RE:NPV Sandstorm's share is....@unlimited, it's even lower if you consider most of the production is during the early years according to True Gold's release: "First full year of production expected in 2016, with production of more than 150,000 ounces of gold projected."
During these years, Sandstorm collects 5k ounces. During the later years when production will be less, they will be collecting the 1.8%.
Quick NPV using a 10% DR gives me closer to $20-21m. They must be counting on exploration upside as well as the potentially exercising the additional $20m financing.