It says the T&Cs at the bottom.
Quote: "For a change of day from the normal club preferred Sunday’s (due only to Sky TV coverage) announced after the season commences, Season Ticket holders will be eligible for the following discounts against a 2015 season ticket if they are unable to attend. The vouchers are non transferrable so must be used by the same person. The initial Sky games announced prior to the start of the season do not apply. Only the ones that are moved away from Sunday after the list is published will qualify. Un-used vouchers MUST be retained by the season ticket holder and handed in at the time of booking their 2015 season ticket otherwise the discount will not be given. The discount will be calculated in line with the category paid in 2014.
The discount only applies to tickets purchased in the Direct Golf and Britannia Rescue Stands and will be £15 for adults, £10 for over 65’s, £5 for under 23’s per game change.'"
