Unfortunately, it doesn't really matter how many cadets CX wants to hire, since they were never enough applicants who meet their standards.
Remember, they do not pick the best 30 out of 3000 applicants every year and put them into the cadet course. They pick the ones who pass the line set by CX.
The lack of quality applicants is the reason why a permanent residency in HK is no longer a requirement.
For this year, only 19 cadets were sent to Adelaide, not 25. There were actually less cadets hired in 2007 than in 2006.