> No statute defines "clean room RE" and there's basically no relevant litigation establishing case law.
It doesn't really make sense for it to be in a statute or in case law.
When you are a copyright infringement defendant the plaintiff has the burden of proving two things: (1) that they have valid and enforceable copyright rights, and (2) that you infringed those rights.
Direct proof of the later is rare, so they usually prove infringement by showing you had access to the work and that your alleged infringing work is substantially similar.
There are some defenses in the statute, such as fair use. With these defenses you are basically saying "Even if they prove everything that normally would prove they case, there is this exception that says in these circumstances I'm allowed to do that". (That's called an affirmative defense).
There are also affirmative defenses that were developed in case law. First sale doctrine was originally a case law developed affirmative defense, but was later incorporated in the statute. Copyright misuse is another case law affirmative defense. That one has not been incorporated into statute.
There are also non-affirmative defenses, often called negative defenses or failure-of-proof defenses. With these your defense it "They can't prove I did this thing that is necessary for them to win".
Clean room implementations are not technically a defense. They are a development methodology designed to provide rebuttal evidence to support a future failure-of-proof defense if you are accused of infringement.
How would you even put that in a statute? As far as case law goes all the case law you'd expect to see is around the particular evidence offered to show the implementers really did not have access to copyrighted elements of plaintiff's work, like record keeping and proof of authenticity and things like that.
An analogy would be like not having alcohol at an event you are hosting that is open to families because you want to make sure you don't violate laws against serving alcohol to minors. You aren't going to find a statute that says "Not having served alcohol to children is a defense to a charge violating the not serving alcohol to children statute". It is implicit in the not serving alcohol to children statute.
Any case law you find on this will not be about whether not serving alcohol to children is a valid way to avoid violating the not serving alcohol to children law. It will be about whether or not some kid that had alcohol got it from you or snuck it in from outside or about whether you took care to make sure your caterer adhered to you no alcohol policy or things like that.