A320Slave and skwinty,
It seems we have a disagreement. A320 says the calibration should be OK to Mach 0.86, skwinty says "the aircraft was completely outside of its normal flight envelope".
While these aircraft may be permitted to fly at 0.86 Mach at high altitude, they are not permitted to fly that fast at low altitude. It seems reasonable to me that the altitude calibration at high altitude would be to 0.86 M but at low altitude they wouldn't need to calibrate to that speed and probably would not bother. As they are limited to 350 knots it seems unlikely that they would be calibrated much beyond that at any altitude.
But unlikely is not proof. Still looking for the documentary proof.
A320, you appear to be unaware that earlier in this thread it was pointed out that the ground elevation was determined at each position report, and added to the radalt height, so a proper radalt altitude was obtained. In the last few seconds before impact there are no buildings which can confuse the radalt.