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Why is this a problem?
It is just because the Trezor doesn’t store any information it does not need to store. Basically it only stores the seed, and then gets all the information it needs from that seed when it needs it.
So when you connect it how would it know which accounts you have added, and which you haven’t? The answer is that it doesn’t. Instead it shares the public key with the suite, which then checks which of the addresses have balance/activity and shows those ones. Therefore it can no differentiate from an empty account that has been added, and an empty account that has not yet been added. And neither does it need to.
This is also why it needs external storage to store for example labels.