It is usually organized by first letter of surname, but not alphabetically. Remember that Italian women almost always traveled under their maiden names. This usually indicated the immigrant didn't have money, didn't have a destination address in the US, or didn't have a friend or relative to meet them. There are undoubtably many reasons attributed to the changes in our Italian surnames upon entrance into the United States. Immigration officials changed the name either on purpose or mistakenly.
Some stories indicate shortening or Americanizing the name to make it easier to pronounce.
An immigrant, having spent a fortune to book passage probably would not speak up against this because of fear of not being let in the country. Poorly written name. This could cause misinterpretation of the proper spelling of the name of the immigrant. Passenger lists can be found at the National Archives. To order copies of the lists by mail you must use NATF Form 81, National Archives Order for Copies of Ship Passenger Arrival Records .