takata - not familiar with the AB system, but I suspect something is 'lost in translation' on this. I would expect the CPC receives a digital 'static' input from AD1/2/3/ and thus if they are either shut down by crew action or isolated by software the source may be lost? Whether there is a backup?
Incidentally, did I see someone claiming the ACARS message could also be cabin alt >8.8k? Is this a revision of the 'definite' claim that it was only an up or down rate signal?