I wouldn't trust that booking engine one iota. I've had any number of booked flights canceled in the past few days, even though they were happily selling tickets for them. Not only KL, by the way.
A quick count shows that about 160 KL-coded flights departed AMS yesterday, Sunday. Although that of course included a substantial number of codeshares, KL is still flying to lots of destinations. All night stops have been canceled, so most departures from AMS are in the morning or afternoon, with all return flights the same day. There were exactly 100 pax on my flight to CPH yesterday afternoon, but only 20 booked on the return.
Johan