Unfortunately, the booking situation at CX is "dynamic", so to say, so long-established rules are no longer guaranteed. When there is availability, just take care to book. Even skip items as seat selection, or whatever, to avoid, the availability disappears.

It's not what it should be, though it is as it is. We should not forget, this whole mess is not CX's fault. The whole China/Hong Kong mess developed in the past 8 years under reign of a great leader and all signs are, there is no end in sight, given recovery is just on the wrong road (see how Russia develops into a complete disaster).