Yes, that's correct. Perhaps you already know, but a few other details:
- The C bucket is both a revenue fare bucket and an upgrade inventory bucket. If you're setting up an alert in ExpertFlyer, be sure to go into the "Awards and Upgrades" section.
- If you're searching for upgrade inventory, be sure to search for availability segment-by-segment, not on your whole routing. (For instance, you could search A->B->C and see upgrade inventory along the entire route. But you need to search for availability on A->B and B->C separately.)