Michael Crichton's novel references a British train robbery from Victorian times:
https://en.wikipedia.org/wiki/Great_Gold_Robbery
The 1903 movie referenced is a separate dramatisation of a US robbery:
https://en.wikipedia.org/wiki/The_Great_Train_Robbery_(1903_...
Re:Great Grain Robbery (1972)
by tragomaskhalos on Sunday April 26, 2020 @04:44AM
(#22985624)
The '63 train robbery indeed still holds an unhealthy spell over britons, part of our broader culture of lauding mavericks who get one over on the system, even if they happen to be unpleasant / violent criminals. Probably the same in the US when put like that I suppose. A less commonly recounted aspect of the Great Train Robbery is how incompetent the perps were and how easily caught
> The term Great Grain Robbery is a pun referring to the "Great Train Robbery" novel
The novel in question being a 1975 one by Michael Crichton! Being British, to me, the term refers to an infamous train robbery in 1963. I don't know if that incident is well known in the US.
Presumably, though, both those uses are references to the film.