1692 - The Crucible
I checked YouTube and Arch Stanton’s grave in the final scene is dated February 1862. I’m not sure if other grave dates are shown.
Some additional nominees for years with existing nominations: *
1863 – Glory
1885 – The Oxbow Incident
1944 – The Longest Day, Anzio
1964 – On the Beach
Unclaimed years:
1925 – Inherit the Wind
1926 – The Sand Pebbles
1928 – The Artist
1952 – Hoosiers
2002 – Moneyball
A bunch of these movies are in that same boat. We know that a part of the movie was set in a particular year, but also set in years around the one we choose. For instance, Breaker Morant. He was executed in February 1902, but the events precipitating the trial were in 1901.
Also, I don’t recall for many of these movies if the year was specified within the movie. We know a historical even happened in a given year, but how sure are we that a movie depicting the event actually says the year?
For 1634, an alternative movie is Ken Russell’s The Devils, which was certainly a more influential and controversial film than Black Robe. Opinions differed on whether it was very, very good or very, very bad. 
For 1876, John Ford’s She Wore a Yellow Ribbon is better known than The Molly Maguires.
Regarding Casablanca, the movie is set in December of 1941 but began filming in May 1942, so I don’t think it qualifies as a “period piece” under the meaning of the OP.
I would relax this criterion for events that took place in the last 10 years, since otherwise we would have nothing but movies set in the future when they were made.
Based on the OP, I’ve been using the criterion that the most significant, important, or climactic parts of the plot unfold in the year in question even if the movie takes place over many years. For example, the climax of Les Miserables takes place during the uprising of 1832, even though the movie extends over several decades. It’s been a while since I saw Breaker Morant, but I think the trial and execution are the most memorable/significant parts of the film.
Per the OP, the date of a historical event depicted in the film is sufficient:
Whether or not an event happens in a given year that the movie depicts, the movie is not necessarily “set” in that year. Even Pearl Harbor, which I wouldn’t dream of calling a great movie of any year. Most is set prior to 1941 – the guy goes off flying for the RAF, gets shot down and goes missing, yadayadayada. And then there’s the depiction of the Doolittle Raid, which is in the following year. Since the movie starts with the two leads as kids, it is set in a period of maybe 15 years.
1665 Girl with a Pearl Earring
1667 The Scarlet Letter
1756 The Mission
Your interpretation of the criteria for selecting movies appears to differ from that of the OP.
Bonnie and Clyde is a confusing one. It refers to real people and real historical incidents that happened over a three year span (1931-1934), but presents them as if they’re happening at a single point in time.
So, as the appointed keeper of the list and the threadstarter, I’m putting Tora! back in for 1941. Not having known how poorly reviewed it was, though (59% on Rotten Tomatoes), I did wonder if Pearl Harbor did merit the 1941 slot, but it only drew 25% on RT. (I did think the battle sequences were pretty epic.) To me, Pearl Harbor is clearly set in 1941, even if there pieces to the film from different years.
I’m sure there are a lot of questionable dates in the timeline – and certainly worthy for debate. But as Joel’s mom says (per the OP), “Just use your own best judgement.”
2005: The Transformers: the Movie (1986)
The latest list:
BC One Zillion BC, October 9th - Caveman
BC 1,000,000 One Million BC
BC 1200 Troy
BC 480 300
BC 326 Sikandar (1941)
BC 72 Spartacus
BC 44 Julius Caesar
33 Life of Brian / The Passion of the Christ
40 Caligula
208 Red Cliff
460 The Last Legion
528 A Connecticut Yankee in King Arthur’s Court
922 The Thirteenth Warrior
1183 The Lion in Winter
1199 Robin Hood (2010)
1242 Alexander Nevsky
1298 Braveheart
1327 The Name of the Rose
1415 Henry V
1424 Andrei Rublev
1431 The Passion of Joan of Arc
1482 The Hunchback of Notre Dame
1492 1492: Conquest of Paradise
1533 The Royal Hunt of the Sun
1535 A Man for All Seasons
1547 Crossed Swords
1558 Elizabeth
1560 Aguirre: The Wrath of God
1597 Shakespeare in Love
1607 The New World
1625 The Three Musketeers
1630 Hara-kiri
1634 Black Robe / The Devils
1665 Girl with a Pearl Earring
1667 The Scarlet Letter
1692 The Crucible
1712 Rob Roy
1756 The Mission
1757 The Last of the Mohicans
1776 1776
1788 The Madness of King George
1789 Mutiny on the Bounty
1791 That Night in Varennes
1794 Danton
1798 The Wild Child
1799 The Marquise of O / Sleepy Hollow
1805 Master and Commander: The Far Side of the World
1808 The Persecution and Assassination of Jean-Paul Marat as Performed by the Inmates of the Asylum of Charenton Under the Direction of the Marquis de Sade
1815 Waterloo
1816 Gothic
1827 Children of Paradise
1832 Les Miserables
1836 The Alamo
1841 Amistad
1854 The Charge of the Light Brigade
1857 Mangal Pandey: The Rising
1858 Django Unchained
1860 The Pony Express
1862 The General
1863 Gettysburg / Glory
1864 The Good, the Bad and the Ugly
1865 Lincoln
1872 Around the World in 80 Days
1874 Blazing Saddles
1876 She Wore a Yellow Ribbon
1877 The Last Samurai
1878 Cheyenne Autumn
1879 Zulu
1880 Stagecoach
1881 Tombstone
1882 The Man Who Would Be King
1884 3:10 to Yuma
1885 Topsy Turvy / Back to the Future III / The Oxbow Incident
1886 Geronimo: An American Legend
1888 From Hell
1891 Sherlock Holmes (2009)
1893 Lagaan
1893 Far and Away
1897 The Gold Rush
1898 A Message to Garcia
1900 Picnic at Hanging Rock
1901 The Shootist
1902 Breaker Morant
1903 Tom Horn
1904 Meet Me in St. Louis
1905 Battleship Potemkin
1906 Ragtime
1910 Mary Poppins
1912 Titanic
1913 The Wild Bunch
1914 The African Queen
1915 Gallipoli
1916 Paths of Glory
1917 Lawrence of Arabia
1918 War Horse
1919 Eight Men Out
1920 Matewan
1921 Sunrise at Campobello
1922 The Great Gatsby
1924 Chariots of Fire
1925 Inherit the Wind
1926 The Sand Pebbles
1927 Singin’ in the Rain
1928 The Artist
1929 Some Like It Hot
1931 Cabaret
1932 King Kong (2005)
1933 Sounder
1934 Pennies from Heaven
1935 The King’s Speech
1936 Raiders of the Lost Ark / The Sting
1937 Chinatown
1938 Indiana Jones and the Last Crusade
1939 To Be or Not to Be (the original)
1940 The Spirit of the Beehive
1941 Tora! Tora! Tora!
1942 Thirty Seconds Over Tokyo
1943 Come and See
1944 Saving Private Ryan / A Bridge Too Far / Pan’s Labyrinth / The Longest Day
1945 Schindler’s List
1946 The Godfather
1947 42
1950 Men in War
1951 The Last Picture Show
1952 Hoosiers
1953 L.A. Confidential
1954 Snow Falling on Cedars
1955 Back to the Future
1957 The Battle of Algiers
1958 The Godfather Part II
1959 Diner / Stand By Me
1960 Grease
1961 61*
1962 American Graffiti / Animal House
1963 One Flew Over the Cuckoo’s Nest
1964 Mississippi Burning
1965 Moonrise Kingdom
1966 JFK
1967 Platoon
1968 The Unbearable Lightness of Being
1969 Taking Woodstock
1970 Apollo 13 / Apocalypse Now
1972 All the President’s Men
1973 Ratcatcher
1975 The Deer Hunter
1976 Dazed and Confused
1977 Summer of Sam
1978 Lords of Dogtown
1979 Argo / Super 8
1980 No Country for Old Men
1981 Wet Hot American Summer
1982 Waltz with Bashir
1983 Heartbreak Ridge
1984 1984
1985 Back to the Future II
1986 The Squid and the Whale
1987 Fargo
1988 Donnie Darko
1991 The Big Lebowski
1992 Primary Colors
1993 Black Hawk Down
1997 Amélie
1998 Escape from New York
1999 Strange Days
2000 Escape from Los Angeles
2001 2001: A Space Odyssey / World Trade Center / Flight 93
2002 Moneyball
2004 The Hurt Locker
2005 Transformers: the Movie (1986)
2010 2010: The Year We Make Contact
2011 Zero Dark Thirty
2013 The Postman
2019 Blade Runner
2022 Soylent Green
2026 Metropolis
2027 Children of Men
2032 Demolition Man
2035 I, Robot
2057 Sunshine
2074 Looper
2084 Total Recall (the original)
2122 Alien
2150 Daleks - Invasion Earth: 2150 A.D.
2160 Avatar
2173 Sleeper
2179 Aliens
2199 The Matrix
2214 The Fifth Element
2274 Logan’s Run
2293 Zardoz
2491 Buck Rogers in the 25th Century
2500 Waterworld
2505 Idiocracy
2517 Serenity
2805 Wall-E
3978 Planet of the Apes (1968)
5021 Planet of the Apes (2001)
12090 Vampire Hunter D
40000 Barbarella
802,701 The Time Machine (2002)
Pretty awesome we can debate the merits of two different movies set in 1634!
1890 - Hello, Dolly!
1896 - The Far Country
1899 - Newsies
1989 Buffalo Soldiers
1990 Rent
1994 Hotel Rwanda
1995 Invictus
1996 12 Monkeys
Yes, but The Molly Maguires has Richard Harris and Sean Connery. SEAN CONNERY!
**
She Wore a Yellow Ribbon** is a decent film, but not a great one, IMHO. And I think The Molly Maguires has aged better. It is still relevant to a modern audience, albeit more allegorically than literally.
1949 - The Man Who Wasn’t There
She Wore A Yellow Ribbon has John Wayne, and won an Academy Award for Cinematography. It is widely considered a classic among John Ford’s films. It outdoes The Molly Maguires on Rotten Tomatoes (although it’s pretty close): 94% vs. 89% Fresh, 3.7 vs. 3.4 rating.
Personally, I find The Molly Maguires a much more interesting film in a lot of ways, but I don’t think it’s necessarily better as a movie.
If this is the case, I suggest that using The Good, the Bad, and the Ugly as an example of a specific 1864 time frame is nebulous. Was there an indication of how long Arch Stanton had been planted or how long they had been looking for the gold? Unless there is more specificity, the movie could have been set in 1862, 63, 64, or 65.
I don’t have a hate-on for TGTBATU (it’s one of my top-10 movies of all time). I just noticed it in the list and wasn’t sure it met the specs of the OP. There are probably other nebulous examples in the list as well.
Umm… yes. But on the whole, the list freaking awesome, IMHO.