Originally Posted by Koby

There will be a lot more trains on sale, but you need to wait a bit longer. (When I said "as soon as possible" I was referring to the tickets being on sale.)

Mid-December most European train companies change their timetables, and the new schedules are probably not finalised/loaded yet. (To get an idea of the number of trains, do a dummy search on Iryo or Renfe for a similar day early December.)