That would be a counter-counterexample, wouldn't it?
* an example supporting the counter-example is simply another counter-example, and
* an example contradicting the counter-example is, by definition, also another counter-example.
Corollary: all examples that can be opposed or contradicted by counter-examples are themselves also counter-examples.
DKIM might have convinced the witness sometimes though.
It is the lawyers appearing before the court that may attempt to play the person not the ball, by variously undermining or bolstering their standing as an expert at all.