Missed that question - sorry (I was writing my reply on a train!)

I don't know how many people were booked on KL1506 as I arrived quite early (to grab breakfast in the lounge), and jumped in a taxi to the triain station the moment they announced the cancellation, which must have been just after 0815. However, I remember that when I checked in (at about T-24) a fair number of seats had been taken including - unusually!- a couple of emergency exit seats. So it can't have been totally empty.

It seems that none of the flght tracking sites have any information about KL1505 (I checked flightstats.com earlier) - maybe someone forgot to update the system with the cancellation? I doubt it ever got to NWI - why would they have announced the cancellation when they did, i.e., more or less the exact time that the flight would have departed from AMS?

The thought did cross my mind, at one point, that they perhaps took the flight to NWI full of passengers and then decided to leave it there for routine maintenance (they have a maintenance base there...)... but I'm sure they couldn't have got away with it as people would have noticed!