GGLwannabe have you looked at the seat plan on one of the many other websites such as Expertflyer.com? They will often show a seat map even when QR does not. Seat map not available could just mean that all seats are occupied but in this case I tend to agree with your 'overbooked' theory.
If you suspect overbooking then you should use OLCI to check-in as soon as it opens 48 hours prior to departure. It will be more difficult to downgrade you if you already have a boarding pass.