Many songs have A and B parts. If we allow combining many different "melodies" to create the larger whole that covers some music in that now you only need to find 8 note, single octave combinations. I don't see why we should allow that, but if you allow it.

8 notes in a single octave pretty much limits you to melodies of someone who has been studying music only a few months. Even my penny whistles are capable of more than that after a couple months of study. (a few days if you already know music or are interested in one specific song)