If you can show any indication that there existed copyright licenses prior to 1980 with explicit dedication to the public domain, then that would indeed show how licensing software under public domain could be a norm before RMS and the free software movement was started.
For U.S. government works however, there was an implicit license of public domain. Works authored by U.S. government employees, on government time and as part of their job, are automatically in the public domain. The purpose of explicit licensing such work would be both unclear, but also questionable in a legal sense. Writing a copyright license for work already in public domain is kind of a grey zone.
As for the 1976 Act, there is to my knowledge no court case about software copyright infringement between 1976 and 1980. The definition of "any greater or lesser rights" when in "conjunction with automatic systems capable of storing, processing, retrieving, or transferring information" is not only extremely vague, there does not seem to been anyone who defined it before congress did it in 1980. If you again has any evidence to the contrary, I would be interesting to read it.
if you want to see early copyright cases for software, Stern Electronics, Inc. v. Kaufman from 1981 is a good example. Note that Konami did not register a copyright of the underlying code of the game, but instead registered the game as an audiovisual.
For U.S. government works however, there was an implicit license of public domain. Works authored by U.S. government employees, on government time and as part of their job, are automatically in the public domain. The purpose of explicit licensing such work would be both unclear, but also questionable in a legal sense. Writing a copyright license for work already in public domain is kind of a grey zone.
As for the 1976 Act, there is to my knowledge no court case about software copyright infringement between 1976 and 1980. The definition of "any greater or lesser rights" when in "conjunction with automatic systems capable of storing, processing, retrieving, or transferring information" is not only extremely vague, there does not seem to been anyone who defined it before congress did it in 1980. If you again has any evidence to the contrary, I would be interesting to read it.
if you want to see early copyright cases for software, Stern Electronics, Inc. v. Kaufman from 1981 is a good example. Note that Konami did not register a copyright of the underlying code of the game, but instead registered the game as an audiovisual.