The setting isn't download safe files, it's run safe files after downloading.
Not even close to the same thing.
And yes, even the existence of such a setting is stupid.
It looks to me like the Copyright Office accepted the renewal. Had they not, the record would/should show the original registration only, and you would be left to compute that since the original copyright was filed in 1954 and was not renewed, that the work was now in the public domain.
Also, the link you posted was for The Broken Sword, not for Brainwave.
"However, even if ‘The Escape” had not been published as a novel, it would have remained under copyright protection until 1981 (28 years) and been eligible for copyright renewal. Authors of that era, and Anderson in particular, were very aware of the need to renew copyrights, and typically meticulously kept their copyright protections up to date. Copyright law for works created more recently is much easier: life plus 70 years. (Sonny Bono Copyright Term Extension Act, 1998)."
-- is irrelevant because as a general rule of publishing in those magazines, copyright was assigned to the magazine. If the magazine screwed up and didn't renew its copyrights; or simply went out of business, in which case no one was tracking their assets; or got bought out by some other entity and the record keeping went all pear shaped, copyright did not magically revert to the author. Nor is there any precedent to have an author reassert their copyright claim on works that have been assigned to others. The instance in which the magazine did not file a copyright is obviously a specialized case.
UNIX was not designed to stop you from doing stupid things, because that would also stop you from doing clever things. -- Doug Gwyn