Jack you may also be interested to know that Calibre has a feature called Fetch Annotations that works only for Kobo readers.
Plug in your Kobo and view:
Send to device (Irrespective that it says 'send' to device, the program copies 'from' the device)
Fetch Annotations (experimental) - it's the last entry
When I've used Fetch Annotations it's been successful - but - they've all been Epubs.
You'll find them in the Metadata section of Calibre - as part of the general book info where you see the synopsis etc of the book.