Issue Tracking Sessions

Hi Kenjis,
Many thanks for your reply and the snippet.
So essentially, I cannot track a session that has been regenerated?
I am also seeing I cannot logout a specific user (unless I interrogate every session for the user id), and I cannot check for multiple logins by the same user, unless their 2nd, 3rd, ... logins are from different IP's?
I'm therefore assuming I would not be able to do any of the above without changing CI core?
Again many thanks :-)