I feel like the consideration that ultimately made the most difference in deciding in the plaintiffs' favor was this rule about including a "significant portion" of one work within another, or something like that. And indeed, the notes in question make up fully half the kookaburra song. But it's so short, I feel like there needs to be a limit. Otherwise you can have people laying claim to whole songs consisting of trivial musical notes or solitary measures. And even if the right short combination of notes can be distinctive, the tune they were fighting over was not the sort that leaps out at you. It went largely unnoticed for 26 years until an Australian quiz show, based on a staffer's original research (as opposed to settled fact), asked contestants to name the similarity.