From your own source . . .
"Judges use four factors in resolving fair use disputes, which are discussed in detail below. It's important to understand that these factors are only guidelines and the courts are free to adapt them to particular situations on a case-by-case basis. In other words, a judge has a great deal of freedom when making a fair use determination and the outcome in any given case can be hard to predict."
The definitions of Fair Use are VERY FAR from being clear.
But here's good stuff from Wikipedia . . .
"United States law in effect since March 1, 1989 has made copyright the default for newly created works. For a recent work to be in the public domain the author must specifically opt-out of copyright. For works produced between January 1, 1923 and March 1, 1989, copyright notice is required; however, registration was not required and between January 1, 1978 and March 1, 1989 lack of notice is not necessarily determinative, if attempts were made immediately to correct the lack of notice. Any American works that did not have formal registration or notice fell into the Public Domain if registration was not made in a timely fashion."
So there might be a loophole for 2600-era games! But it'll probably never go to court because both sides would spend more than they could gain.