Skye, I'm just as surprised as you to see R on an international flight. I remember that there was quite a discussion last year about whether the new electronic VIPs would be using "R" inventory internationally -- but the consensus was that they wouldn't be starting to do that just yet. Someone else may remember the details better than me....

I am quite certain, though, that "R" is the correct class for using the 500-mile "stickers" for upgrades to business class in North America. (For example, on the LAX-JFK run, with lots of business-class seats, "R" will print out on your boarding pass if you upgraded using the 500-milers.)

A couple of observations regarding why "C" shows as 0 when the seatmap shows seats. First of all, the seatmap is a notoriously bad predictor of how full any given cabin is -- seats may not have been assigned, but have been sold, thereby making the map look like there's open seats when they have actually been sold (just not assigned). Also, as you said, they may be holding the seats back from upgrades, and the seat(s) may or may not be "released" for upgrading closer to departure....