I want to book a train from Visp to Milano Centrale on September 17th. The timetable shows there is a direct Eurocity train from Visp to Milan, but all the time i couldn’t make a reservation. When I tried different dates in July or October, I could find available reservations, so why is September 17th fully booked? Is it possible that reservations will open up later if I wait, or is the train fully booked for that date?