Ah, so the main key does a gift wrap to send the backup to a new pubkey, thats why the relationship between these two keys is private?
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And thus even if the main key leaks, the backup keys are not known.
And if you need to access the backups just giftwrap them with yet another key so that they backup key never leaves the backup client.
Yep, the main key doesn't have any gift wrap to recover from.