After it's original airing in 1965, A Charlie Brown Christmas went through multiple changes the following year in 1966 to improve things that the original crew were not happy with due to the limited time they were given to make the special and due to the fact that the special was considered a failure at first by most behind it until it became a massive success and would be aired again the following year. These 1966 changes have been the definitive version for the crew behind the special and all subsequent airings and home media releases leaving the original version almost completely lost and unreleased to the public.
- The song Christmas Time Is Here starts earlier than in the 1966 to present version to allow the full song to be heard instead of fading out once Charlie Brown hits the tree. The dialogue was relaid and the start of the music was pushed back farther in the later version
- During the main title shot the sound effects are differently pitched, both the wobble of the tree and the plop of the snow, after Charlie Brown crashes.
- Snoopy throws Linus into a Coca Cola sign and the song fades out with "Christmastime..." repeated several times.
- Disproving rumours, the can that the characters throw snowballs at is NOT a Coca Cola can.
- Less sound effects during Lucy's psychiatric booth scene.
- When Snoopy decorates his doghouse "Christmas Time Is Here" plays instead of the more upbeat "Surfin' Snoopy". During this, Charlie Brown's voice from the Disneyland/Vista read-alongs is spliced in the soundtrack, then quickly reverts back to Peter Robbins' voice.
- When Charlie Brown is greeted as director, Snoopy's howling sounds more realistic and wolf like.
- There's no music playing in the background during the director scene until the 'Linus and Lucy" dance.
- When rehearsing, Lucy gives "five good reasons". But in this version, we don't see a close-up of her hand.
- There's no 'Blah" sound by Snoopy after licking Lucy.
- Snoopy's dish is white in the rehearsal and the sound effects are normal clanking sounds.
- There is little to no music during the rehearsal scenes.
- The long shot of the characters dancing on stage is played for an additional time. In the 1966-present version, they're in their costumes in separate shots.
- Lucy's fingers don't make a snapping sound when she likes the music.
- When Charlie Brown tries to find a tree Linus doesn't bang on the aluminum tree.
- Either a live-action or intergrated Coke commercial plays after leaving the tree lot.
- The scene with Schroeder and Lucy goes as normal, but there's no music, nor does Schroeder make a drumroll sound while spinning.
- Linus' speech is intact.
- Once Charlie Brown is eager to decorate the tree there is no fade out to commercial. That was added in the 1966 version. It just immediately cuts to Charlie Brown's shock of Snoopy winning first prize. Also, Charlie Brown's mouth moves differently.
- Charlie Brown blushes while singing after the tree is decorated, and Snoopy sings like a human instead of making a howling motion.
- The song Hark The Herald Angels Sing does not fade out but concludes with an onscreen message saying "Merry Christmas from the people who bottle Coca Cola".
- There is no "The End" copyright screen, it was apparently added in 1966 after the studio realized that the special would be airing more than once.
- There's a spot afterwards where Charles Schulz thanks Coca-Cola for sponsoring "A Charlie Brown Christmas".
Besides the Paley Center for Media the only way to access a print of the original version of the special is by acquiring a print from a private collector. Besides the two Coca Cola sponsor plugs, the entirety of the original version has never been made publicly available on the internet. It is doubtful this version will ever get a home media release.
UPDATE: An original print of the special was shared as an MKV to the Lost Media Wiki. A comparison video with the two prints is available on YouTube and Vimeo.
Book: "A Charlie Brown Christmas: The Making of a Tradition"