They've definitely held back a good number of GA seats for match-day sales, as they didn't want there to just be upper tier back-rows (and lower tier front rows) left available for those (more expensive) on the day tkts.
Also, a friend of mine is beginning to suffer quite badly from arthritis, but was in one of the later tranches (due to waiting for his son to be eligible). He told the club about his worsening medical condition and his concerns about having to climb too many steps to the only available seats. They invited him down and he was offered seats that he said were definitely not available on the seat map (near a vomitory) in the South Stand.
Maybe they put them aside for less able-bodied people in the later tranches, or maybe they're just part of that bigger number of seats being kept aside for matchday sale only.
I would be surprised if there weren't some match-day tickets set aside for the hospitality sections too. They could probably charge a decent mark-up on those too.
