JAL hardly overbooks flights. Their seat control technique is an art. But I did have an operational upgrade once on NRTBKK. They seem to take account of your attire and the agent seems to have a considerable authoritiy in giving you an upgrade. Not automatic according to elite statsu unlike U.S. airlines. This is an impression I got from what I experienced and what I heard from friends. Anecdoal, that is. Good luck.