Note list duplicates (numbered) -- how to prevent?

Hello! I'm using Joplin 2.9.17 on Windows 10, 64 bit (full version info at bottom)

In my note list, I see many notes that seem to be duplicates or older versions of notes with the same title. They have a number in parentheses at the end of the note title. For example, I have a note called "Events" and another called "Events (1)". I didn't copy or duplicate notes, and I didn't add the number. Joplin seems to have duplicated these notes and added the numbered versions. How can I prevent Joplin from doing this? When I edit a note, I only want the new (edited) version kept.

Detailed version information:
Joplin 2.9.17 (prod, win32)
Client ID: 0570b41d09af4c84a9455eb8e550719b
Sync Version: 3
Profile Version: 41
Keychain Supported: Yes
Revision: a84a8e7

Have you ever exported some or all your Joplin notes (made a backup) and then imported it back in?

If so, Joplin treats the imported notes as new notes. If an imported note title is a duplicate of an existing note title it appends a number afterwards. This can be avoided by not importing a backup into Joplin when Joplin still contains those notes.

Thank you, dpoulton, but although I've exported all my notes several times, I've never re-imported after exporting. I wonder if it's possible the duplicate notes could be a side effect of synchronizing between PC and smartphone??

It shouldn't be as keeping the notes up-to-date between clients is what syncing is all about. I am afraid I have no suggestions for you as to what may have happened here. I have only ever seen this occur when a backup has been imported into a Joplin client where the notes already exist.