One big trick and tipp:
Never use KL`s websites/booking engines !!
It is just that simple, not only that the websites are slow and just bad, the booking engines are not worth a penny.
If you like to get a real quote on the availabilty, you have to call the Helpdesk !!
OK, I have to admit that you sometimes get good information on KL flights, but if you look for availabilty on NW, you can just quit it, waste of time !!