HarryJ,
Thank you for your comment. I've sadly found this problem on several airline websites, although usually not from top-tier airlines like Cathay Pacific: as there is no disclosure about how many of the advertised seats are actually available, the traveler never knows what the supply is. The airlines know well that once people check their calendars and get a set of dates for a desirable destination in mind, they may still want to buy even if the original deal is not available.