When I create a new wallet, how is it prevented that the seed already belongs to an existing wallet? S.
I think it's by sheer probability alone. At least that's how Bitcoin wallets work, and they only have 12 seed words for each wallet. We have 33 words per seed, so the possibilities are exponentially higher. I'm no statistician so I'm not going to throw in any numbers here (maybe @Shadowlance can help with that), but this video does a great job at explaining the concept.