the dealer can tell you the build date by the VIN number, of importance is the replacement of the compression spring that was in the earlier models. On this forum their were a few that had a smoking issue on the 2016. The machines otherwise are identical. I priced both and decided since had green for the last 3 Yamaha's, went with a 2017 Blue addition for a change of pace. Since the last machine lasted 13 years, this might be the last ATV for me.
The 2016 has the reverse lock cable that needs the brake engaged to shift to reverse or park. the 2017 does not have this OH SO annoying feature. Its pretty easy to modify and override it, and I think Yamaha realized people hated it and removed it (Finally!).