Over years of migration of Onenote pages, I ended up in sync issues and duplicates. This is now less relevant as OneNote is capable storing in the cloud. So the sync issues almos gone. But 10 years ago, when OneNote was not such known it could be synced at file level only. E.g. hard drive to USB or to network share.
Finally, there is free utility to remove duplicate pages on OneNote. It worked for me and saved hours of manual cleanup. After cleanup, I moved my all notes to the cloud.