Specifically, where MarkKnopfler.com is able to secure 1000 seats for a single show, there may be more than one price point of ticket in that inventory for that show. If there are only 600 of the most expensive tickets then the remaining 400 have to be the next best available and they are generally a little cheaper.
Fair Admission would randomly assign all 1000 seats in the inventory to shopping carts and send them out. The people who get the shopping cart have until October 27 to complete their purchase. A majority of people will not complete their purchase. So, a majority of those 1000 seats will be available in the October 29 presale. The presale will be exactly the same as all previous MarkKnopfler.com pre-sales.
People that receive shopping carts do not check out for a number of known reasons that may include: having requested multiple shows and only want to attend one, having seen the ticket price decide it is too expensive, changed their mind, etc.