One of my holy grails was a workprint of Thomas and the Magic Railroad. That film was infamously heavily edited following negative response from test screenings, resulting in the replacement of several members of the voice cast (Thomas was originally voiced by a resident of the Island of Man [where they filmed the Sodor scenes] who was a part-time taxi driver and firefighter and James and Percy were both voiced by Michael Angelis, who was the UK narrator for the series at the time, but all their voices were replaced because the American test audiences thought they sounded 'too old' and Diesel 10 was originally voiced by Keith Scott but his voice was replaced because they thought his voice was too scary for kids. They also replaced the voice actor for the characters Splatter and Dodge no one knows 100% why he was replaced nor how much he had recorded for the characters) and, most infamously, the near-complete removal of the character of PT Boomer, a human character who was supposed to be the main villain of the entire film. I say 'near-complete removal' because Boomer is still in two scenes in the final film: there's one scene where another character is talking to someone on a motorcycle and that character is Boomer (with his voice being redubbed) and you can see him on top of Diesel 10 during the final chase scene. There were also some other minor changes like the film was supposed to be narrated by the character of Lily as an adult instead of Mr Conductor.
And this editing genuinely was very last minute. Keith Scott's Diesel 10 audio was used in trailers for the film and PT Boomer not only appeared in the film's theatrical trailer, but he was also in a Japanese trailer, appeared in a couple of tie-in books, and was supposed to have a (cancelled) figure as part of the line of die-cast toys.
So for years, people were trying to find this mythical workprint/director's cut of the film once it became known how much was edited, just to see what the original version was like, especially because one of the most common complaints is how disjoined the theatrical release of TATMR was. (Like a good example of this is during the final chase scene, the character of Burnett Stone tells Diesel 10 that he won't win because 'the magic you refuse to believe in will get the better of you'. The problem with this line is that it's very clear in the film that Diesel 10 believes in magic. He's talks about how Mr Conductor's magic railway is going be over and later on he even tells him that he knows all about the buffers and the magic railway as well. Of course, in the original cut, this line was being delivered to PT Boomer who, even when he's literally interacting with the sentient and talking locomotives still thinks they're nothing more than giant toys) We'd get crumbs here and there like some of PT Boomer's scenes were leaked and the 1999 script was found and archived as well. But the full original cut? Nope, people were still hunting for it.
Then back in 2020 someone found and uploaded the original workprint online and, later that year, the deleted scenes were included on the 20th anniversary BD/DVD release from Shout Factory, so there's that grail having been found and is now watchable.