The flight number is still QR4851 but now operated by JAL not Qatar as originally scheduled. The departure time is different (now 23.30 compared to 23.55). I may well call BA as the booking was a one-way Avios redemption (HND - LHR via DOH) to see if I can get the seats sorted. Also, I have read that JAL do not allow seat selection with certain fare types or only allow so many seats to be pre-allocated - but I am confused by that as I managed to reserve the seats for the PVG - HND flight with JAL previously.