So, in other words, if you don't distribute a derivative work you are fine.

Like I said. The point stands once again. Everything that you said only applies for distribution of copies. And if you don't distribute copies, and you don't sign any contracts, you are fine.

> This requirement of the GPL has been enforced by courts

You have misunderstood that court case. Nobody can be forced to follow the GPL. Instead, you can only be forced to pay damages for distributing copies.

Following the GPL is simply a method of avoiding damages for distributing copies. But you don't have to follow it. You can simply either not distribute copies, or you can pay damages for your distribution of those copies.

So the point stands once again, that you cannot be forced to follow these contracts, and you can only be prevented from distributing copies.