@machinbird
The programming was inadequate for this condition of being airborne with very high AOA.
Yes that must be true. It is a case where the "requisite imagination" failed to envisage such a case as a necessary condition. But if some engineer had dared to suggest before publication of the AF447 DFDR traces that the aircraft might be driven into a 42 deg plus AoA situation and held there by pilot action they would have been howled down with scornful cries of "You are not a pilot" and "No pilot would do such a thing". I find it difficult to accept that the designers and their test pilot colleagues acting ten years earlier would have any reason to conclude differently.
There are a number of things that could have been done to determine how much stall AOA correction for Mach was necessary, but since it wasn't written into the code, it didn't happen.
As you say, it wasn't written into the code so it didn't happen, but it is not obvious that it needs to happen. If you are at 45 deg AoA or more it hardly matters whether the threshold for warning is 8.6 deg or 17.2 deg. The warning should be sounding.
I think you are missing a point however. If the warning were to be latched until safe conditions were restored (as suggested by BOAC and myself) the airspeed indications would necessarily be restored to normal and the proper stall warning threshold for the Mach number computed before the warning would be cancelled. You will remember that when the AoA was reduced temporarily the airspeed came back on line and the stall warning with it. That is why I think your next suggestion -
If, for example, the aircraft could compare g to measured AOA, it should then have been possible to estimate IAS with sufficient accuracy to set flight control gains as well as estimating Mach number based on OAT and altitude.
is an unnecessary complication.
In any case, when NCD was encountered while airborne, the stall warning AOA should have at least been set to the backup value of 8.6 degrees and not just turned off simply because the airspeed didn't make sense.
Yes I agree with you there.