They require three pieces of information in all cases, but where it is available, they require a set of other information such as passport number, the airline's internal numbers used to monitor the ticket, the passenger and so on. There are seven or eight elements, and we could read them to you.
In my opinion, the confusion stems from the fact that, for virtually all flights, although not all, all pieces of information are required. However, for all flights, they gather the three pieces of information required by the U.S. Department of Homeland Security, that is to say name, date of birth and gender. For example, if I travel on a friend's small personal aircraft to go fishing in Maine, that friend will not have to provide all the other pieces of information because he does not belong to a commercial U.S. airline. He will nevertheless have to state the names, dates of birth and gender of the people who accompany him.