A lucky clerical snafu
It's a Wonderful LIfe - January 7, 1947, general release in the USA.
The movie, It’s A Wonderful Life, premiered at the Globe Theatre in New York City on Christmas Day of 1946 but didn't appear in theaters until January 7, 1947. Even though it was nominated for five Academy Awards, including Best Picture, it received mixed reviews and was unsuccessful at the box office.
In 1974 a clerical error prevented the copyright owner from filing the necessary extension application. The movie went into the public domain. This allowed any television network to show the movie without having to pay costly royalties. The film was shown repeatedly every holiday season for almost 20 years, solidifying it as a Christmas classic.