I am not an attorney and any comments I post are not intended, nor should they be construed, as legal advice. If you need legal advice, please consult a legal expert who is familiar with the area of legal expertise you need.
I talked about this project early last month – Millions of Books Are Secretly in the Public Domain. You Can Download Them Free. Don’t assume that any book in the 1924 – 1963 time period is in the public domain. From the article, around 75% are, but that still leaves 25% that are not in the public domain. Using the links from my earlier post and the link below, you may be able to determine if a specific book is or is not in the public domain.
Here’s an update – Libraries and Archivists Are Scanning and Uploading Books That Are Secretly in the Public Domain – September 10, 2019: https://www.vice.com/en_us/article/a3534j/libraries-and-archivists-are-scanning-and-uploading-books-that-are-secretly-in-the-public-domain.