this was a CO B fare which matches to NW B and is NW metal, SEA-NRT. Opushomes is reporting that this is non-upgradeable with miles, as it is CO-ticketed, even though NW-operated. This is not written out anywhere at nwa.com, and is a little disappointing, since there does appear to be availability and I've got miles to burn.

sorry, I realized this thread was regarding SWUs and not miles, but I wanted to clarify that this fare included NW metal flights, as well.