A project I was involved in while working for the USGS Publications Warehouse I was involved in a project were a number of documents that were ultimately not put into our collection because of copyright concerns. Because most of the full text publications Pubs Warehouse are government documents (our library creates metadata for journal articles that we link to using a DOI as well but this doesn’t involve copyright concerns) our digital library does not often worry about copyright issues. But during the cataloging phase of a large digitalization project the Pubs Warehouse cataloguers realized that a number of the publications that had been digitized were contracted works in which either a private company or another federal agency had written a report for the benefit of the USGS. Copyright concerns kept the private contracted from being entered into the library along with the consideration that our library only has the mandate to post works published by the USGS.
If the works in this project had been written before 1964 there would be a fairly good chance that they would be be in the public domain by virtue of a copyright not being renewed. But the reports in question were all published in the 1970‘s.