Echoing two of the above two posters, JAL does not overbook in F.
Just because you cannot select a seat in F (be it award or paid ticket) does not mean that it's not available. As mentioned previously, they always leave at least one seat for VIP or some such usage. If they can sell you a seat, there'll be at least two seats opened at the time of your booking. 1A (and sometimes 1K too) are the two that are most often blocked off. So, maybe count yourself lucky, you just might be getting one of those two seats
(of course, that might not be your preferred seat...)