If you define NCAP_START=2018, investments into the process will normally be available only in periods T such that M(T)≥2018. In other words, if you define NCAP_START=2018, investments into the process will NOT be available in period 2017, assuming M(2017)=2017.
I would suggest to set NCAP_START=2017, to enable investments already in 2017, because you are expecting that the capacity is coming in period 2017. Alternatively, you can set G_OFFTHD(T)=1, which will cause investments into the process to be available also in periods T such that (NCAP_START – B(T)) / D(T) < G_OFFTHD(T), and so they would be available in 2017 even if NCAP_START=2018.