You're too forgiving. CAN has offered 72 hour Transit Without Visa since August 1, 2013. Six months should be plenty of time to have things working correctly. And prior to that, CAN certainly had the 24-hour flavor of TWOV...which also had implementation problems that were purposefully anti-passenger enough to be more than incompetence. Since the Chinese are usually quick learners when they want to be, and Guangzhou isn't known for being full of idiots, my conclusion is that there is some sort of internal inter-departmental disagreement or intransigence going on at CAN and TWOV passengers are sometimes caught in the middle.