It is my belief that both of the initial volumes of Magistrates of the Roman Republic are in the public domain. They were published prior to 1964. Even though copyright was asserted at the time of their publication, that copyright was not renewed within 28 years of publication. See for details:
- https://guides.library.cornell.edu/copyright/publicdomain
- https://fairuse.stanford.edu/overview/public-domain/welcome/
The second volume of Magistrates of the Roman Republic has a post-1980 entry on Copyright.gov. However, the basis for the claim is only to the new introduction. Moreover, because this was registered after the original work published in 1952 already fell into the public domain, it cannot revive any such copyright.
The third volume of Magistrates, however, published in 1986, is definitely still in copyright. If that copyright was retained by the author and not assigned – as it appears the original MRR copyrights were – this third volume would remain in copyright for the lifetime of the author + 70 years. T R S Broughton died in 1993, meaning that the third volume leaves copyright in 2063.
I assert no copyright over the text of Magistrates vols 1–2. Any copyright here asserted applies only to the code and commentary.