Possible Clues:

• Ticket-buyer who stayed home (perhaps wisely)
• Reservation reneger
• Ticket holder with a conflict, maybe
• Like Godot numbers? In what way?
• Someone who neither keeps nor cancels an engagement
• How after son has turn reservation goes missing
• Non-attendee
• At last, exhibition on Rising? Sounds like promoter's worst nightmare!
• Runaway bride, e.g
• One failing to appear as booked