Maybe your moodle administrator is not keeping the logs indefinitely, as I do. In moodle, one can set the Standard Log to "Never delete logs."
I think if "Nothing to display" shows, that student never logged into any course. I believe that this would happen if the student's account was never confirmed.
You could also access the actual moodle database, and look at the mdl_user data. I notice a field for "firstaccess." It's a little harder to read, and this field has some coded data in it. In my moodle, my own entry shows "1447381900", so you would have to dig a little deeper to decode this date. This process takes you much more into the guts of moodle, but the database has it all. Depending upon your need, you might hire someone to create a custom SQL query.