Hi,
This is irrelevant. The BEA is fully mandated by the law for investigating those data which are staying (from the begining) under judiciary control (those Gendarmes are in charge of the recorders and a judiciary police officer is always staying with them). So, the BEA doesn't own those "evidences" and work on them following its mandat. What is released for the public is in the BEA report, as per the law.
You right .... this material (the black boxes) are exhibits to the prosecution of the court process.
The BEA report (the result of their analysis) is not an exhibit.
It therefore not falls under the same sections of law protecting the exhibits.
That's the point I want to put emphasis (BEA report is not part of the judicial process)