These would be reduce the problem at the airport. When passenger show up at the airport without any information of the irregularity such as flight cancellation or re-schedule the flight, passenger might ask for the compensation and this would cause a lot of expenses. I would recommend us seriously to develop a system to inform passenger in irregularity case by setting a mandatory in PNR when passenger bought ticket. A mandatory would not allow an agent to create a booking without passenger information such as contact number.