Yes, as if 23000 fans get tickets reserved for them for the final, any loyal fan who can't attend the game for whatever reason will have a hard time getting one, especially considering any season ticket holder with a stub can buy two.
Also, your idea wouldn't work as if every season ticket with a stub did indeed buy two tickets, this would pretty much be our entire ticket allocation for Cardiff gone anyway, which would mean the other 8-10000 attendees wouldn't be able to definately gain a ticket.