Not knowing what spots you are referring to, it's a little difficult to pin point the exact reason but I can give you some general insight: Spots are often delivered in multiple time formats to give the advertiser flexibility when purchasing media. read more
After air, the schedule is reconciled with the as-run log. A traffic system is the heart of a station and has a database with every commercial and when it should play. After as-run reconciliation a traffic system will see a spot that did not play and can automatically fix that by rescheduling the spot in another qualifying time-slot. read more
Commercial Broadcasters may not exceed 18% of their broadcast day on advertising and they may only have a maximum of 12 minutes of adverts per hour, except for children's programming where advertising may not exceed 10 minutes per hour (commercial TV broadcasters include TV3 and Setanta). read more