As ilovejedd said the info is stored on a sidecar dir, they will be stored in koreader/history if the path is read only.
KOReader was hacked on top of a filemanager and lacks the concept of "library".The best way to emulate one is to parse all metadata. This will give you info for any book that was opened at least once.
https://github.com/noembryo/KoHighlights is a standalone tool that does that very well (iterate over a path looking for metadata).