Glenbuck i think was ridden in an Intermediate section but he has too many points for that class so he has to be ridden HC.
He can be competitive in OI classes, which is open for horses with more points. Same as all the other Open classes, OPN, ON and now Ointro. Its open for horses who have too many points or wins for that level.
So like i riding in an OPN class means I can be competing against horses that have been round badminton who are competing in the same class.
Before Open Intro classes, all riders who have ridden at Advanced werent allowed to be competitive in Intro classes so had to run HC.
Also, if classes are full but someone is desperate for a run they can run HC.
Does that makes sense
Also, note that OI is NO different to an I class. The fences are exactly the same and the dressage test is the same. Its just that the horses in the OI section have too many points to be competing in a straight I section.