Checklist for if a book or magazine might be public domain

First of all, I am not a lawyer, and so this is not legal advice. I would recommend that if you are interested in copyright terms in the United States, you read Circular 15a from the US Copyright Office

If it is a paper document (book, magazine etc) that was published more than 95 years ago, then it is out of copyright (in 2022, this is 1926, and it goes up every year until 2071, when it gets more complicated because the US laws changed in 1976/1977)

For the years till 1963, if the copyrights were not renewed, then it might be out of copyright (note that there is no completely reliable way to check that something newer than 95 years is out of copyright, since part of it could be based on something that is still in copyright). Here is my checklist for finding things that might be out of copyright

1. Published in 1963 or before
2. Published in the United States (The title page better include a United States city for the publisher, and nothing that says published in Great Britain or other country)
3. Search the Stanford's Copyright Renewal Database and make sure it is not found in it. Note that it only lists books copyrighted in the United States.
4. Search the Library of Congress Copyright Catalog. Note this includes magazines and other things besides books, but it does not include renewals before 1978, so anything published 1950 or before will not be in here (and you could renew early, so 1951 or nearby could also be missed)

If you are trying to find a book that might be in the public domain, most of these checks can be done from the information in a library catalog or a used book site. Different book subjects have different probabilities of being renewed. For example, of the math and physics books I have checked, 90% or so were renewed. For computer hardware books, only 10% or so were renewed. I have checked five difference scientific conferences (over a hundred articles) and have yet to find a paper in them that was renewed. Also, if you have a bibliography, you can do these checks with the information in the bibliography and if they pass you can then see if you can get a hold of the book, article or magazine.

If the renewal requirement hadn't been eliminated in the 1980s, I suspect there would be a lot more books in 1964 and later that would have become public domain, but are currently out of print and getting harder to find.