My understanding is that copyright is only honored by the legal system if it's been enforced by the copyright holder. If the copyright holder knows its being u

My understanding is that copyright is only honored by the legal system if it's been enforced by the copyright holder. If the copyright holder knows its being used, and doesn't attempt to enforce copyright rights, but after a decade or similar, changes mind and starts enforcing, the court might rule that copyright is no longer enforceable.