Question: In what year did the historical film drama based on the true story of Charles Horman win The Palme d'Or?

Context paragraphs:
Missing (1982 film): Missing (stylized as missing.)  is a 1982 American historical drama film directed by Costa-Gavras and starring Sissy Spacek, Jack Lemmon, Melanie Mayron, John Shea, Janice Rule and Charles Cioffi.  It is based on the true story of American journalist Charles Horman, who disappeared in the bloody aftermath of the US-backed Chilean coup of 1973 that deposed the democratically elected socialist President Salvador Allende.  Set largely during the days and weeks following Horman's disappearance, the movie depicts his father and wife searching to determine his fate.  The film examines the relationship between Horman's wife Beth (Spacek) and her father-in-law, American businessman Ed Horman (Lemmon).

Stealing Heaven: Stealing Heaven is a 1988 film, a costume drama based on the French 12th century medieval romance (a true story) of Peter Abelard and Héloïse and on a historical novel by Marion Meade.  It was directed by Clive Donner.

Captains of the Clouds: Captains of the Clouds (a.k.a. Shadows of Their Wings) is a 1942 Warner Bros. war film in Technicolor, directed by Michael Curtiz and starring James Cagney.  It was produced by William Cagney (James Cagney's brother), with Hal B. Wallis as executive producer.  The screenplay was written by Arthur T. Horman, Richard Macaulay, and Norman Reilly Raine, based on a story by Horman and Roland Gillett.  The cinematography was by Wilfred M. Cline, Sol Polito, and Winton C. Hoch and was notable in that it was the first feature length Hollywood production filmed entirely in Canada.

That Hamilton Woman: That Hamilton Woman, (also known as Lady Hamilton and The Enchantress), is a 1941 black-and-white historical film drama, produced and directed by Alexander Korda for his British company during his exile in the United States.  Set during the Napoleonic Wars, the film tells the story of the rise and fall of Emma Hamilton, dance-hall girl and courtesan, who married Sir William Hamilton, British ambassador to the Kingdom of Naples.  She later became mistress to Admiral Horatio Nelson.

Diane (film): Diane is a 1956 American historical film drama about the life of Diane de Poitiers, produced by Metro-Goldwyn-Mayer, directed by David Miller, and produced by Edwin H. Knopf from a screenplay by Christopher Isherwood based on a story by John Erskine.  The music score was composed by Miklós Rózsa, and Robert H. Planck was the cinematographer, who filmed in CinemaScope and Eastmancolor.  The exceptionally lavish costumes were designed by Walter Plunkett.

1982 Cannes Film Festival: The 35th Cannes Film Festival was held from 14 to 26 May 1982.  The Palme d'Or was jointly awarded to "Missing" by Costa Gavras and "Yol" by Şerif Gören and Yılmaz Güney.

Oliver Twist (1912 American film): Oliver Twist is a 1912 silent feature film drama based on Charles Dickens's classic novel Oliver Twist.  This film is the first feature version of the story followed a later British film released in October 1912.  Nat C. Goodwin, a distinguished comedian from the Broadway stage, stars.  The General Film Company, usually a distributor, produced this film and it was released on State Rights basis.

Joyce Horman: Joyce Marie Horman (born December 3, 1944) is an American human rights activist.  She is known as the wife of journalist Charles Horman, who went missing in 1973 while the couple was living in Santiago, Chile.  Her search for what happened to him was chronicled in the 1982 film "Missing", in which she was portrayed by Sissy Spacek.  Spacek was nominated for an Academy Award for her performance as Horman.  Her family's story was first told in the 1978 book by Thomas Hauser titled "The Execution of Charles Horman: An American Sacrifice".

Double Danger (1938 film): Double Danger is a 1938 American crime drama directed by Lew Landers, using a screenplay by Arthur T. Horman and J. Robert Bren based on Horman's story.  The film stars Preston Foster and Whitney Bourne, with supporting roles by Donald Meek and Samuel S. Hinds.  Produced by RKO Radio Pictures, it was released on January 28, 1938.

Elizabeth Horman: Elizabeth Dorothy Horman (December 30, 1904 – May 10, 2001) was an American fine-artist.  She was also known as the wife of businessman Edmund Horman, and the mother of Charles Horman, a journalist that was killed in Chile in 1973.  The events of her son's death were chronicled in the 1982 film "Missing".

Supporting paragraphs: 1982 Cannes Film Festival Missing (1982 film)
Answer: 1982