Once upon a time, there was no home video market and practically no reruns. In a very infamous case, the BBC deleted the master tapes of many of its television programmes up until the late 1970s, with the most notable casualty of the practice being Doctor Who.
Fortunately, there are no actual missing episodes of Scooby-Doo. However, I have been left the impression that some of them do not exist in their original form. Let us see.
Scooby Doo Where Are You! - I'm aware that Turner and Cartoon Network have remastered the episodes. This could logically mean that the original recordings have been purged. A possible exception is "Go Away Ghost Ship".
The New Scooby-Doo Movies - From what I've read, several (or all?) episodes have scenes that were cut, in order to solve the TV stations' financial needs, I suppose *sarcasm*. These scenes are not on the DVD/Blu-Ray releases, so they may been destroyed for real.
The Scooby-Doo Show - the original intro for the Dynomutt season has been seemingly lost, except for the soundtrack... just like with many of Doctor Who's early episodes. Apart from that, there is the episode title card mystery and that whole rough cut business in Season Two.
That's it for now. If you have any more information, please share.
I believe "Scooby-Doo, Where Are You?" and "The New Scooby-Doo Movies" originally did not have master tapes. Being animated shows from 1969-1973, they were presumably fully edited and then printed on film, as during that time it was not uncommon for TV stations to receive film prints of TV shows (usually in 16mm) and air them via telecine techniques. Same with "The Scooby-Doo Show." I believe many of Hanna-Barbera's shows from the 70s were printed on film for distribution. And I also remember a scene that was cut from reruns of "The New Scooby-Doo Movies" episode "Guess Who's Knott Coming to Dinner" was restored onto the DVD release (a three-minute sequence where Scooby ends up sneezing from a pile of dust and flying into the fireplace, where he thinks going up the chimney may be a secret passage.) As for "Scooby-Doo, Where Are You?" when Warner Home Video released the show on DVD in early 2004, they actually went and restored the episodes from the original negatives in high-definition, in a manner not unlike they have for the Looney Tunes cartoons for those Golden Collection DVD sets of the time. (Restored in high-definition because they knew that would soon be the future of home video, saving them the trouble of having to remaster them all over again years later, even if they were to just be released initially on standard-def DVDs.) They retained scenes cut from syndication, the laugh tracks, and the original Hanna-Barbera closing logos, but replaced the original early Ted Nichols instrumental theme tune with the more familiar vocal one. These were also used for the Blu-Ray set and the Boomerang streaming service (the latter cutting out the H-B logos.) Plus, I do know that the time-compressed late 80s/early 90s syndication recordings still exist, since Boomerang has used them for their previews and such...
If anything, the 1996 Turner remaster of "Go Away, Ghost Ship" must have been the one that was purged or damaged, which is why post-2007 TV reruns of that episode reverted back to that older time-compressed syndication print.
Ah, I must have gotten the episodes mixed up then, as it was the other way around with "Go Away Ghost Ship". Is that the one where Velma still sounds like a chipmunk?
It's slightly strange that WB would go to the trouble of restoring the early episodes and not put the original instrumental opening theme. There may be some truth to the theory that Ted Nichols is not to be acknowledged at all - unlike Hoyt Curtin, who even got his tracks published... but not Nichols.
I think a purist would have liked seeing the episodes as they were originally broadcast, but I digress.
Anyway, thanks again and that music from the end of the scene above is now stuck in my head.