Licensing guidance for government forks of open source projects

[greenlaw]

I am part of a team working on a software project that was originally based on a codebase we received from a non-US entity with a BSD 2-Clause license. Since that time, extensive changes have been made, to the point where 99%+ of the code is new and bears no resemblance to the original work. We're now at the point where we'd like to release this project on GitHub, but want to make sure we get the licensing right.

Our team currently consists of contractors operating under FAR 52.227-17, though we may receive contributions from federal employees in the future.

Based on my limited understanding, even though the work is almost entirely different from the original, I believe we must retain the original BSD 2-Clause license, including the original copyright notice, but since the Government has not taken assignment of the copyright from the contracting company, we can't include a U.S. Government copyright notice.

Rather than dual-licensing with BSD and CC0, we currently think the best way forward is to just retain the BSD 2-Clause license (with original copyright), and perhaps just include a clarifying statement in the README about the lack of U.S. government copyright.

The one relevant resource I found linked from project open data is the CFPB Source Code Policy, Section 2b, which seems to agree with our plan:

Software source code previously released under an open source license and then modified by
CFPB staff is considered a "joint work" (see 17 USC § 101); it is partially copyrighted,
partially public domain, and as a whole is protected by the copyrights of the non-government
authors and must be released according to the terms of the original open-source license.

However, if anyone has encountered a similar situation, I would appreciate any additional input/recommendations you could provide before we move forward in the next couple weeks.