The original Scooby-Doo, Where Are You instrumental theme by Ted Nichols aired during the opening titles for "What a Night for a Knight" and "A Clue for Scooby-Doo" when they originally aired in 1969, instead of the theme song with lyrics. After the original airings, the theme song with lyrics that was used for the other 23 episodes replaced the instrumental intro in all rerun airings of "What a Night for a Knight" and "A Clue for Scooby-Doo." The instrumental theme for those two episodes was not heard again until 1990 when the episodes aired on the USA Network. The copy of those two episodes that used the instrumental was shown again during reruns throughout the 90s. In 1998, Turner remastered all of the Where Are You episodes, but used the copies that used the theme song with lyrics for those two episodes. Since then, the instrumental intro for those two episodes has not been used in any airings. All home media releases for those two episodes include the theme song with lyrics.
Despite this, the original instrumental theme is not completely lost. The instrumental theme was repurposed as the music that plays during the title card. It was also repurposed (and extended) for background music in two episodes of season 2, "Mystery Mask Mix-Up" and "Jeepers It's the Creeper."