OK. That means tehre are only two things which can explain it:
1.) The notebooks were not shared correctly
-- OR --
2.) They were shared using another MS account, not the one used on OneNote Online or Windows OneNote App
I decided to test this again, starting from scratch. I installed Windows 10 Pro on a test machine, and Office 2010 to that machine. I created some sample notebooks storing them locally, on computer.
I then shared the notebooks with my own MS account email, and closed OneNote 2010. Going to OneNote Online, the notebooks were immediately available. They were also immediately available in Windows OneNote App.
I am sorry you can't make it work, cannot think anything else I could tell you. The instructions given are for 100% sure correct, that I have now tested several times.