Well this is certainly a new twist. I tried it to see what the hitch is and it certainly can be frustrating. Tried OMA-CUN week after Thanksgiving, a routing that NW serves via all three hubs 1xdaily. But the award booking engine routes through IAH on codeshare with CO.

But you don't get the error message UNTIL the last booking screen. You would think that the red flag would go up on the first screen when no NW-only options. The other laughable thing is that I found a couple of options with PerkSaver in F or PerkPass in Y. Let me see...book F for less miles than Y, hmm...

I think when I use my 615 promo that I'm not going to even bother checking online. I'm just going to call to book it. They must have learned this from DL!