When does my contract end?

My contract start date was August of 2012. My contract states I'm enlisting in the Navy Reserve for 8 years and my nsips states my contract end date is August 2020. My NOSC is saying that I have to drill for the full 8 years because the only date showing up for them in August 2020, no date to start IRR. I enlisted in the NAT program and in the first line it states that I'm enlisting for 8 years, 6 of which will be active drilling status and the remaining 2 years IRR. Shouldn't my end date be August 2018? Does my NOSC not understand my contract? I can't seem to get a 100% accurate answer.