You got lucky to take the fastest Tsubasa Service! I viewed the JR East Shinkansen Timetable carefully and saw that Yamagata Shinakensen Tsubasa Train 131 (leaves Tokyo "Union" Station at 9:25AM Japan Standard Time) stops at the fewest stations unlike all the others. From eyeballing all the other Tsubasa members on the timetable, I found that they make additional stops at Ueno, Utsunomiya, and Koriyama.
