Absence of evidence isn't evidence of absence. "Not getting sued" doesn't validate a legal theory - legal theories are validated in court where they become case law. Until then, they are plainly speculative.

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.