http://www.nwa.com/worldperks/elite/...vSoldOutFlight

NW only appears to offer this benefit for economy class seats, not business. And, they only appear to offer it on international long-haul flights of 6 hours or greater length.

Depending on where you need to go in Asia, they might be able to get you on MSP-NRT, but if NRT-XXX is less than 6 hours, they might be within their rights not to sell you the whole trip.

So, if you're willing to fly Y, it looks like you might a case and you should call back and ask to speak to a supervisor if necessary. But it doesn't look like the benefit extends to J.