Notes has Google Notes. But Google has no such service. Where are they stored? If you go to System Preferences -> Internet Accounts and add a Google account, you can see Google has Notes. If you open Notes (OS X app), it somehow retrieves the notes I had put long long time ago on a different Mac. So, I am sure those notes are not locally stored. Not only can I see old notes, but I can also add new notes to Google Notes.

Google had Notebook service, but it was discontinued long time ago and existing notes were imported into Google Docs. But I cannot find the notes I see in Notes in Google Docs.

So where are the Google Notes stored and Notes is getting the notes from? Is it that Google discontinued the web interface of the Notebook service but somehow still provides an interface to Apple especially? Can I access the notes I saved to Google Notes in Notes outside the Notes application, in a web browser for example?
The notes created in OS X can be found in GMail under the label "Notes". If you create a folder with [name] in OS X Notes app, the notes will be synced to Google Inbox unbundled label "Notes/name".