Chunkyman good question. Not sure on if they will ask the information on msg in a bottle and woods through the Larian vault or through the survey.
I would assume they will do it to the survey since they will be asking all sorts of questions like delivery address (for physical goods), t-shirt sizes, etc so everything related with your KS pledge.
Also since they need to know if you need a GoG or Steam key etc.
But don't hold me to that, I think we'll just have to wait and see what happens and give Larian the time they need to sort out how they want to do it.