Quick question: on what basis does the BEA reports that the speed measurement became valid again at 2:12:21 ?
2:12:21? No, not then.
The report states that
about 15 seconds after 2:10:51, the ISIS speed measurement abruptly jumps to 185KT, at which point it is consistent with the other recorded speed (ie the LH speed, as the RH speed is not recorded). It notes no further disagreements between the two recorded speeds for the remainder of the flight; rather, it notes that at various points that "all recorded speeds became invalid" (presumably when they fell below 30KT) or became valid (climbing above
60KT), indicating that they remained consistent with each other.
If I'm not mistaken, with at least two consistent speeds, they would be considered reliable even if the third (which was not recorded, and so we don't know if it differed) was different.
[edited to correct error on min speed at which speed is considered invalid; 60KT, not 30KT (see BEA report, note at bottom of p.2 of French version)]