No element of "Night of the Living Dead" has a copyright on it - they recently did a remake that had absolutely no affiliation with the makers of the original.
"It's A Wonderful Life" was never public domain.
As Wikipedia notes:
"...a clerical error at National Telefilm Associates prevented the copyright from being renewed properly in 1974. Around this time, ... a popular fallacy began that it entered the public domain and many television stations began airing the film without paying royalties. ...
For several years, it became expected that the movie would be shown multiple times on at least one station and on multiple stations in the same day, often at the same or overlapping times. ... In 1993, Republic Pictures, which was the successor to NTA, relied on the 1990 U.S. Supreme Court ruling in
Stewart v. Abend (which involved the movie
Rear Window) to enforce its claim of copyright; while the film's copyright had not been renewed, it was a derivative work of various works that were still copyrighted. As a result, the film is no longer shown as much on television (NBC is currently licensed to show the film on U.S. network television...), the colorized versions have been withdrawn, and Republic now has exclusive ancillary rights to the film. Artisan Entertainment (under license from Republic) took over home video rights in the mid-1990's, Artisan was later sold to Lions Gate Entertainment, which continued to hold home video rights until late 2005 when they reverted to Republic's sister studio Paramount, whose parent is Viacom."