A lap infant is still a passenger in the airline’s records
A ticket does more than reserve a seat. It links a traveler to a specific flight and its passenger list. So when a baby travels on an adult’s lap, the airline still needs the infant recorded as a passenger—even though no separate seat is assigned.
That record helps the airline know who is aboard and carry out procedures that depend on an accurate passenger list. If the flight changes, staff also need to know that the adult is traveling with an infant, rather than treating the adult as a party of one. A lap arrangement changes where the baby sits; it does not make the baby disappear from the flight’s paperwork.
A ticket does not necessarily mean a separate seat
The infant’s booking is tied to the accompanying adult, but it identifies the child as a traveler in their own right. Charges vary by airline and itinerary, so an infant ticket does not necessarily cost the same as an adult fare. The key distinction is between paying for a seat and having a valid booking: the infant may use the adult’s lap while still needing that booking.
That is why “one seat, two people” is not a loophole in the passenger count. The seat is shared; the flight’s record of who is traveling is not.
