It's not just your Nintendo Account that latches on to one Switch at a time -- your game saves are stuck, too. Nintendo has quietly posted word that saves are stored exclusively to the console's built-in storage, so you can't just transfer your progress to another system like you could (however awkwardly) with the Wii U or 3DS. If you're determined to complete Legend of Zelda, you'll have to finish it on the system where you started.