Well, even though The National Film Registry is meant to preserve up to 25 films deemed “culturally, historically or aesthetically significant” each year (since it was established in 1988), therefore it has had 425 chances to preserve each of the 68 Best Picture awarded films, it has yet to add 34 of them, half of all of the Best Picture winners.

In fact, if you take a look at the breakdown by years apparently a lot of real crap has been slipping in for far longer than anyone realized.

These are the films which won Best Picture but are not (yet) in the US National Film Registry. The films in parenthesis are films which are in the USNFR and were also nominated for best picture that same year.

Academy Award for Best Picture

1928–29: The Broadway Melody
1930–31: Cimarron
1931–32: Grand Hotel
1932–33: Cavalcade (42nd Street, I Am a Fugitive from a Chain Gang, She Done Him Wrong)
1935: Mutiny on the Bounty (Naughty Marietta, Top Hat)
1936: The Great Ziegfeld (Dodsworth)
1938: You Can’t Take It with You (The Adventures of Robin Hood)
1940: Rebecca (The Grapes of Wrath, The Great Dictator, The Philadelphia Story)
1942: Mrs. Miniver (Magnificent Ambersons, Yankee Doodle Dandy)
1945: The Lost Weekend (Mildred Pierce)
1947: Gentleman’s Agreement (Miracle on 34th Street)
1948: Hamlet (Treasure of the Sierra Madre)
1952: The Greatest Show on Earth (High Noon)
1956: Around the World in Eighty Days (Giant, The Ten Commandments)
1963: Tom Jones (America, America)
1964: My Fair Lady (Dr. Strangelove or, How I Learned to Stop Worrying and Love the Bomb)
1966: A Man for All Seasons
1968: Oliver!
1976: Rocky (Network, Taxi Driver)
1979: Kramer vs. Kramer (Apocalypse Now, All That Jazz)
1980: Ordinary People (Raging Bull)
1981: Chariots of Fire (Raiders of the Lost Ark)
1982: Gandhi (E.T. the Extra-terrestrial, Tootsie)
1983: Terms of Endearment
1984: Amadeus
1985: Out of Africa
1986: Platoon
1987: The Last Emperor
1988: Rain Man
1989: Driving Miss Daisy
1990: Dances With Wolves (Goodfellas)
1991: The Silence of the Lambs (Beauty and the Beast)
1994: Forrest Gump
1995: Braveheart