ACD's can do well in any of the AKC courses. I honestly don't know of any dogs titled on the C course. Simply because of the props/land/roads etc they have to have to put on a trial with a C course.
ACD's originally took cattle to feed lots/slaughterhouses across the outback. Major areas in Australia are very far apart. People would own a ranch with 2500 cattle and drive them to a feed lot that was 200+ miles away. The dog would need the stamina to drive the cattle all day, and continue this until they got to the destination. I'm really trying to paint the picture for you of why ACD's are built they way they are and why they herd differently than BC's. None of this applies to corgi's I know nothing about corgis. At the feedlot the ACD would be needed in close quarters to move the cows into chute's, hold them in position if needed, etc. So essentially an all-purpose herder, but the main focus was driving.
What I'm trying to get as, is while an ACD can do any of the AKC courses, it doesn't truly test their original purpose. If there were such a test, there would be about 8 guys on horseback and about 6 dogs herding cattle from Dallas, TX to Houston.
That would be a sight!