This "clean room RE" fabrication is also not something so obviously compelling that nobody would ever attempt to challenge it - it's just that nobody has cared to put dollars behind it. IP provenance cases are enormously difficult to prove and are almost always settled ahead of trial. This concept is software engineer folklore more than anything.
I seem to recall DeCSS being the 'hot button' as it was RE'd in a 'non clean' way, the code released, and then a 'clean room' RE could be made from the 'public' info ??
edit: actually, at the time I think there was German law allowing RE for 'interoperablity' or some such. But that was a long time ago so my memory might be off.
It's safest to err on the side of plausible deniability, any proximity to OEM software increases liability if things go wrong.
For the record Yuzu included code for circumventing Nintendo's DRM they had on game carts. It violated the DMCA.