Thanks for your answer. I have some further questions
1. So Beijing to Shanghai night train is bookable online in advance means we could now
book for the 15th of December?

2. Is it possible to book the train to Yandang in advance as well or just at Shanghai Station a couple of hours before we leave (16th of December)

3. What do you think, will tickets from Yandang to Shanghai (19th of December) still be available when we arrive at Yandang the 16th of December?
Last Summer I wanted to go by train from Beijing to Shanghai and they said the trains were sold out for two weeks.
Thanks.