I'm not sure it was sloppy writing by Puzo (who also wrote the script with FFC -- so if there is blame here, it should equally fall on the both of them) but just dues ex machina to set up the hearing and the Hagan visit at the end of the film.

Plus, as with many other instances in the film, there are small gaps in logic that are neatly placed in the film to allow our imagination do the connecting. It could be sloppy writing, but I would like to believe it is intentional... which is why these movies are considered some of the greatest of all time and we are still discussing the films to this day.