Due to any unwanted circumstance such as incorrect migration, space issue.. etc, you may lose one note files. Fortunately Microsoft one note have automatic backup (out of your regular backup application) that keep certain numbers of files till the retention you have specified.
These settings can be configure from one note application itself.
Open one note, select File from menu list, select Options then select Save & Backup.
By default the backup location is typically configured to user profile unless if not change by user/administrator.
From this location you should see different section and backup copies. Select latest copy then open in one note then right click select Move or Copy option OR you can merge with any existing one note section.
Life saver option who use one note