One of the points the PP made was that when he went up for the Preferred Seating, there were already other guests (non-Preferred Seating, AFAIK) taking up the front-row seats.
Sounds to me like, from that post, that those who did have PS had to sit/stand behind those other guests who were
already there before the call-time of the PS group.
Regardless, even if the DID hold the seating are for PS guests, the PS is not held every day or for all parades.