Wikipedia maintains a list of films now in the public domain. de Havilland's films are of the right age to be on the list, but don't appear to be. Most of the films on the list got there from failure to renew the copyright, a requirement which has since disappeared.

> Prior to 1988, all motion picture films published after 1909 with a copyright notice where the 28th year of copyright would occur before 1988, had to be registered and before the 28th year, the registration had to be renewed, or the copyright for the film would expire and it would enter the public domain. This would apply to all films registered for copyright prior to 1960. Copyright renewals became optional in 1988.

https://en.wikipedia.org/wiki/List_of_films_in_the_public_do...