You did a factory reset?
I know that my S Notes are being backed up via Samsung because when I activated my S4 all my SNotes showed up on it not long after. I did not have dropbox set up to save them so I can only assume they were backed up through my Samsung account.
I know the horse is out of the barn now but I suggest an app called Folder Sync, which lets you specify any folders on your device and sync them with any of several cloud services. Won't bring back what you lost, but will prevent a repeat.
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