Which shows how well the series was scored and spotted. Episodes like "For the World is Hollow," "Lights of Zetar" and "Requiem" (with the exception of the new Brahms pieces) were all tracked with library music and scores from other episodes. Yet very often the tracked music works insanely well in episodes it wasn't specifically written for. The third season has a much more somber feel because of the music. "Spock's Brain," for example, has a very dark score and is tracked a great deal throughout the season.
Speaking of "Spock's Brain," I wish Fred Steiner had recorded an unused, expanded version of "Spock's Fugue." How amazing would that be?