Ok, so here's some sketchy business (and leaving my previous post up as photo evidence). I figured out that xliioper'ssearch results are coming up by switching to a nonstop search, since I guess only KL operates nonstop IAD-AMS. That gave me the same 75k results that he/she posted.

So then I got curious and clicked into Dec 23, which shows a 75k result in a nonstop search and an 80k result in an "All Flights" search. The KL nonstop for 75k was nowhere to be found. Only 80k DL with connections. Even worse was Jan 3, which only showed 320k DL redemptions. Both of these dates have 75k nonstop KL available.

Even if you search for the single date directly, and use IAD instead of WAS - basically restricting the search results as much as possible other than specifying nonstop, DL.com will not give you the cheapest and most direct option - instead it will just dump on DL-operated flights at higher prices. You would have to know that nonstop flight is there and specifically look for it in order for the KL flight to appear.

What's even worse is that for Jan 3 in particular, if I restrict to nonstop to find the Jan 3 date, and then click on it from there, the nonstop restriction falls off in the results and I see both the KL direct and a bunch of connections, including a handful of IAD>CDG>AMS options also for 75k (but relegated to the very bottom of the "best match" search results). Ridiculous!