such a common mode degradation would not be detected initially and would fool the system into believing that the A/C was traveling faster than it really was.
Difficult to know. All depends on the nature of icing/ice accrual, which we may never fully know/understand. My guess would be that the crew may have known for some time before AP disconnect that something was wonky with their KIAS. Now, in the a/c that I fly, it would take me, oh, I would say, a few seconds to suspect that something was up with the pitot-static system. That is because I have the luxury of flying a non-FBW a/c. I can't comment on how Airbus drivers are trained to respond. Are the bus drivers at this point thinking "is it the probes or is it the computer". Remember, they probably are not expecting ice at FL350. If this kind of 'thinking' occupies the pilots for, say, a few minutes, we can begin to understand how they can be distracted/fixated. Then we are back to the nature of the ice build up and how aggressively automatics responded.