'FGD' I imagine that was exactly the problem for the hapless drivers, the F/D bars where telling them to go that way (up) due false info to the F/D's, this is where it's time NOT to believe yr instruments, that's at odds as to what we have been taught from day one. If only they had tried the FPV display as that's not effected by blocked Pitot tubes, only if the static ports where blocked.
Blocked static ports ruin everything in a plane, that's the nasty one!
The conditions need to be met as you mentioned (which is obviously correct as you said) is with everything in life from the fuel gauge in yr car to when the LE slats drop out on a Tiger Moth, certain conditions need to be met for it to happen.
The words 'only if'......
At the very least such discussions as this one prods the mind into thinking about 'what if'
Wmk2