@SLSD As you probably already know, "belt and suspenders" is always a good approach. Let Seabourn know ahead of time; there should be a place in your "preferences" selection to indicate dietary requirements. Then, when you board, ask to see the Chef and/or Assistant Maitre D' responsible for special diets, and discuss your needs. The Assistant Maitre D' will bring the next night's dinner menus to you at dinner so you can select what you would like to have and the kitchen can prepare it for you. Then, you can be surprised like we are since we usually do not remember what we had ordered the night before.
The Assistant Maitre D' is also usually good at tracking you down if you are not eating in the Restaurant to give you the next night's menu.