Following something of a fiasco where the firm G4S, the World's largest security company, failed to deliver the required number of security staff for the Games, large numbers of the British military were drafted in at the last moment to assist the operation. Part of the reward (and also driven by a further scandal where large numbers of seating reserved for sponsors failed to be occupied, to the exasperation of true fans who had been unable to secure tickets), was that those servicemen were allowed to occupy unused seats during their breaks. This resulted in tickets such as those below, with no designated seat, which were then distributed to members of the Armed Forces to occupy whatever seats were available.
The press tickets appear the same as the military tickets above, bearing no seat number, but requiring accreditation before access would be allowed.
Different sport athletes
Due to the scale of the Games, no Olympic athlete would be required to be training or competing for every moment of the two week schedule. Each country's Olympic association would be provided with a selection of tickets to each event to allow their athletes to enjoy the Games as any other fan and to cheer on their compatriots. Such tickets appear like that below, requiring the individual's athlete pass to allow entry. If you look closely, you can see the reference to 'Different sport athletes' by the trail leg of the depicted runner.