[HarryT]

As people will of course be aware, publishers update books from time to time to fix issues, etc, and, most of the time, the updated book will automatically be sent to the device it was originally sent to. If, however, you no longer have that device (or no longer use it), this won't be the case.

I'd suggest, therefore, going to your "Manage Your Content and Devices" page at Amazon from time to time, and paging through your library. If a book has an "Update Available" message alongside it, first click the update message and click the "Update" button on the resulting dialog box, and then click "..." and send the updated book to your current device.

I have about 3000 books in my Amazon library, and this only takes me a few minutes to do. I do it at the start of every month, and generally find that about a dozen books have been updated.

Well worth taking the time to do.