The electronic barriers, where you scan your ticket, won't let you in.
Until this year, when you made an online booking, it generated a brand new ticket for you. If you scanned your pass, instead of the online booking, you were scanning a "new" or different ticket from your booked one. The systems are now linked. Your pass is linked to your booking, your booking is linked to your pass. If, on a sold out day, you rock up with just your pass and you haven't made a booking, the gates will not let you through.