That is unless a Marco Polo Diamond Club member has also requested for those seats!

Don't know how CX manages seats... but on SQ for example, if certain seats have already been booked when a PPS Club member calls, he/she may request for his/her favorite seat be put on waitlist (even though he/she has a confirmed reservation - though not his/her favourite seat). If another PPS Club member also requests for the same seat, when the seat becomes available, the SQ computer reservation system will determine the seniority of the seat waitlisted by 1)Highest Tier, 2)Longer PPS member, 3)Highest number of accumulated miles! So it will depend if CX has any MPO members on hold for those seats too!

But then again, look at BA where seats 1A/1K are permenantly blocked off for their GOLD members until check-in.