We are flying NRT-ICN today, booked in I as the flight was originally scheduled to be a 2-cabin plane. It has since switched to a 747, but no F was on sale. When we arrived at the airport we were informed we could sit in the F section of the plane (C service though).
The fact that we got the semi-upgrade could be due to us continuing on F (O) tickets tomorrow. C does not seem to be overly empty (C7 according to EF).

What was weird was that CI agent told us that upstairs was economy class - which I don't see in any of the seatmaps I could find.