Any other interpretation would mean trade secrets have essentially infinite protection/NDAs apply to all of humanity.
The NDA doesn't apply to people who haven't signed it, but copyright law does. If you know the material you're receiving is under copyright (eg proprietary source code), and you publish work based on that copyright material, the fact that it's now widely available is not an effective defense against claims of copyright violation.
Person B in this scenario hasn't violated the NDA, but they could be sued for copyright infringement.
Which I think you know, so I don't understand your argument.
You said in another comment "However, this specific thread is about the scenario where an employee has inside knowledge and is passing that knowledge on to the implementer."
It being proprietary and/or secret information doesn't affect the copyright of the clean-room output. If there's trade secret implications those are worth discussing, but as a separate issue.
A clean room implementation by people who haven’t seen the original work means there can be no discussion of copying, which makes it much cheaper and more reliable to fight an infringement claim.
Your last comment said person B could be sued for copyright infringement. But the essence of clean-room is that person B "hasn't seen the original work which means there can be no discussion of copying".
Person A is not giving the original documents to person B, they only give functional details.
One of your earlier comments had a vague description of clean-room that wasn't clear on this aspect. But you were responding to someone that gave a clear and correct definition, so I assumed you were also using the actual definition.
If you've actually been talking about fake not-really-clean-room then sure someone could get sued. But that's obvious. The suggestion by alightsoul was actual clean-room.
Once it's established that person A has given _any_ details to person B, the upper bound on "expected cost of an effective defense" is dramatically higher.
Yeah but that's what clean room is.
You said "A clean room implementation by people who haven’t seen the original work means there can be no discussion of copying, which makes it much cheaper and more reliable to fight an infringement claim."
Something doesn't add up.
If you were thinking about a situation where the developers don't get the original work, and nobody feeds them info based on the original work either, that's not clean room, that's something much harder.