My daughter is Vegan and we came off the Nieuw Statendam a few weeks ago. Indeed you do have to pre-order which is not ideal as you may decide a day later that you are in the mood for something else. Also it was the same menu each evening so got a bit boring. Our Dining Steward was amazing and would let her see the options from the main menu from the next day as well,as there are occasionally Vegan options on the main menu. Personally, I wish they would offer a few extra vegetarian and vegan options on the main menu each evening. I can imagine the complaints if meat eaters only had one option each evening on the main menu!
During the cake away event on the Lido, there were so many beautiful cakes but none Vegan. I mentioned it to the Executive Sous Chef who was standing nearby and he said he did have one vegan chocolate cake and arranged to bring it to the Lido and personally served the first slice to my daughter! It looked so good that others wanted a slice as well! He told me he would make sure that in future there would be a vegan option included each time.
In short, it’s not easy to eat vegan, often not varied, but ask and they will help you!