[bluepeter]

Some of my e-books are bought from Kobo, whilst others are bought elsewhere. Copies of the ones bought from Kobo are:
(a) downloaded directly from Kobo to my Kobo e-readers; and also
(b) downloaded to my computer and held in Calibre.

(Books bought from other sources are also held in Calibre. These books are sideloaded from Calibre onto the device.)

When I connect an e-reader to the computer, Calibre reads its contents and tells me, in the LH column, which books are on that e-reader. However, there are a few books that it fails to recognise (about 1% of those bought from Kobo, I think). An example is shown in the attached screenshot. Although Love and Other Crimes is on the attached e-reader, there's no green tick.

Removing the download from the e-reader and then downloading it again from Kobo has no effect. I did that with Love and Other Crimes a few minutes before taking my screenshot. I haven't checked, but my impression is that it's the same few books that Calibre doesn't recognise on all of my Kobo e-readers.

Does anyone know why certain books aren't recognised and if there's any way of correcting this?