I'm unaware of it ever having been tested and upheld in court in a SoT situation. And while it's easy to argue that it should be upheld because that's what the license says, it's also just as easy to argue that it shouldn't. Because it's easy to argue that a chain of derivation loses all meaning under copyright law once there are no recognizable elements of the original work. Quite simply, making a claim of copyright infringement requires elements of the original being used. If no original elements exist, then no license can bind, no matter what path it took to get there. Just because you put something in a license doesn't mean it's enforceable.
Yes, I think it's pretty clear (though yes, a lawyer can bring anything up). The basis is the propriety code case I mentioned which has been well litigated over the decades, its clear definition of "derived work" (in particular for the ToS case, not calling into it) and the implication of derivation vs clean room (discussed by others in this thread).
When people try to attack the GPL in court it's typically over it being a contract of adhesion, enforceability, or applicability of calling into it (none of which are an issue in this discussion). The aspects I mention above are too well trodden.
(I'm talking about the USA only, of course, and I assume you, the author of the post are too).
I'm unaware of it ever having been tested and upheld in court in a SoT situation. And while it's easy to argue that it should be upheld because that's what the license says, it's also just as easy to argue that it shouldn't. Because it's easy to argue that a chain of derivation loses all meaning under copyright law once there are no recognizable elements of the original work. Quite simply, making a claim of copyright infringement requires elements of the original being used. If no original elements exist, then no license can bind, no matter what path it took to get there. Just because you put something in a license doesn't mean it's enforceable.