Originally Posted by
railroadtycoon
However, on the Shinkansen and limited express trains, the green car is reserved seating only. The conductor goes through each car with their tablets, so they know which seats are reserved already, if they see someone sitting in a seat that hasn't been reserved or reserved later down the line they will check to see if you have a reservation.
I think you're right, and I definitely defer to the comments of the more experienced travelers above - including the lack of need for green car generally.