See, when I were a youth, by this point in December you could have seen It's a Wonderful Life half a dozen times, on various stations, by now. Mostly the PBS affiliates, but even ABC in Chi would dredge it up, if I remember a'right.
This was because it was believed at the time that the film was in the public domain, and anyone with a print could run it however much they wanted without owing nada to nadie.
And then, once the film's status as a Holiday Classic was assured, mostly by those infinite repeat viewings, it somehow got un-public-domainified.
According to this here article:
We have litigated this issue often: a derivative work, if thrown into the public domain, does not affect the copyright of the original work. For example, if the film CATCH 22 fell into the public domain for whatever reason - the copyright on the original Joseph Heller novel work would prevent anyone from selling, exhibiting, distributing, etc. the film.
Likewise, the film IT'S A WONDERFUL LIFE is a derivative work, according to the present copyright holder, from, among other things, an original short story and/or script. Indeed, most if not all films are considered derivative works - they derive from copyrighted screenplays, theatre, books, etc.
[. . .] The film IT'S A WONDERFUL LIFE is not - REPEAT IS NOT IN THE PUBLIC DOMAIN - and everyone in the biz recognizes that now. Even though many once believed that the film itself lost some copyright protection, and at some time, the market was flooded with broadcasts and videos, today it is accepted that the copyright holder of the original work still controls all film rights to the original work. Thus the film, a derivative work, cannot be sold, distributed, copied, broadcast without the consent of the copyright holder of the original work.
So, technically, it wasn't un-public-domainified. It was never really in the public domain. It's just that everyone and his uncle thought it was.
Now you know, and knowing's half the kaiju big battel!