In my quest to learn composing simple game music I thought I should study some old Mario songs because the simplicity of never having more than 3 notes at the same time
When looking at old chip tune music, you really should consider any technological limitations at that time. The NES could stream four channels and one was used for both music and SFX (which is why some of the music would drop out if you were getting a lot of coins at one time). So that really left three channels of steady music streaming. The composers at this time knew all of the limitations and wrote music to accomodate those limits.