Recently back from a 3-week janut through Asia.

When I bought my ticket, I used miles to upgrade from Y to C. A few days later, noticed my intra-asia segment out of NRT showed me in NF. Of course, wasn't going to complain. Checked in for all flights no problem.

On my SEA-NRT segment, I got a peek at the manifest taped to the galley while I was chatting with a FA. Noticed something disturbing below my name on the list, something to the degree of:

"Paid Y NRT-SIN, in NF. Add/Collect difference." (basically the jist of it)

This was, of course, long before I even got to NRT. Was worried I'd get taken aside when trying to board in NRT, but nothing. Had my first wonderful experience in a F Suite for the price of Y.

Does UA have the right to collect this? It was nothing of my own doing. I gave my miles for C, didn't ask for F, and didn't expect F. Nothing was added to my Amex, and not worried now...But had I been taken aside in NRT, I would have been put to Y, as C was overbooked, and F was full too.