The opening credits list a copyright date of 1947, but distributor RKO rushed IAWL into theaters December 20 1946, to replace 'Sinbad the Sailor' whose Technicolor prints were not ready. It went into general release January 1947. The rush probably cost Capra and his partners their indie studio Liberty Films, whose first production opened in a record blizzard back east and failed to make back its money; it also wound up losing out at the Oscars against a powerful postwar drama 'The Best Years of Our Lives' rather than facing a much weaker Oscar field in 1947. Then again, confusion over its copyright date seems to have allowed it to slip into public domain for about 20 years from 1973, leading to its constant (cost-free) play at Christmas time, cementing its reputation as America's favorite holiday movie.
The scene in the bar where Jimmy Stewart is crying and saying "please God" was originally not shot as a close up. Capra shot the scene, then asked Stewart to act the scene again for the close up shots. Stewart didn't think he could reproduce the emotion, so Capra actually blew the scene up frame-by-frame.