It is important to be aware of the difference between backing up and syncing your data, two very different processes that if confused can lead to data loss.
Backing-up is a process by which data is copied from one location to another for storage purposes. This stored data can then only be changed if the user opens the storage location and actively changes or deletes the data. When backing up your work on Nebo you can either back up a single page or the whole notebook.
Syncing means that changes made to data stored in one location will be immediately reflected across all the devices or locations where that data is accessible or stored. So, for example, if you change or delete a notebook on an iPad that is syncing with another device or with iCloud, that change will happen across all your devices and in iCloud.
Read how Nebo syncs your notebooks: About the sync feature