Well, the problem with determining the flaps/slats possition is that the CVR *DOES* show the crew announcing the flaps/slats as 11º/deployed, so now it becomes a matter of refuting their "word" against the machine's indications.
A different story would've been if the crew never mentioned the wing configuration as being "ok". Then, there is not such a large need to proof the telemetry recording as right, since nobody is challenging it.
So from the judiciary point of view, it has to become as clear as possible why the pilots (seemed to) believed that the flaps/slats were out. Thus the painstaking research into establishing their position beyond "reasonable doubt", if possible, determining stuff such as whether the lever was actuated at all or not, or if there is any possibility that the indicators could show the wrong possition, etc, to challenge the crew's "final words" that the wings were set to go as recorded in the CVR.
Otherwise, anyone in the know understands there is just no way the wings could've been set or any indications pointing to that matter being shown to the pilots and that the crew simply forgot to set them as it happens every-so-often in the world and that they answered the challenge call without really looking at the indicators, as I'm sure is not the first time it happens either.
But this has to be "proven", which is always hard to do with 100% certainty and thus, the benefit of the doubt is always given.