I'm traveling on a NH codeshare ticket in a few weeks that I purchased via UA. I was actually able to select seats on UA's site during the purchase process, despite the fact that the flight is on NH metal.

However, I was not able to purchase an upgrade to Premium Economy, and when I checked the seating chart on ANA's site yesterday, it showed Premium Economy as completely full. My suspicion is that they simply do not make those seats available until they know how many status upgrades they'll have.

One question: is there any chance I'll have the opportunity to purchase an upgrade to Premium Economy at the check-in desk the day of my flight? If so, any idea as to cost (it's an ORD-NRT segment)?