The US Copyright Office contains records of registered works and documents since January 1, 1978. This includes online records and copies of the records and deposits of the Copyright Office. Under the Freedom Of Information Act, federal agencies are required to make all records publicly available and the Copyright Office is no exception.
"The Copyright Office records authors' and other claimants' claims to copyright in original works of authorship and maintains records of these copyright registrations as well as materials deposited with copyright applications for registration (e.g., a copy of the work), records relating to the copyright application process (e.g., correspondence between the Copyright Office and the applicant regarding the application or deposit); recorded documents (e.g., copyright assignments), records relating to the statutory licensing of copyrighted works (e.g., statements of account), and other records regarding the Office's general operations." - US Copyright Office