Trouble is the Indonesian incident looks like the capt went off piste and carefully pulled CB's on two computers one at a time probably thinking that one was always available. He forgot the need to toggle on/off buttons presumably. Perhaps indicates he was aware that two off equalled switch to alternate but was confident he avoided it so not the focus of immediate attention given the roll surprise.
Aural presumably wouldn't get attention so something BIG which needs crew interaction to acknowledge? Don't recall the mode degradation called out on the AF447 transcript. Two very similar sequences would seem to indicate that the human computer interface is not great at convincing of stall or off impressing that the mode had degraded.
Seems that there is no standard procedure for voicing acknowledgement of mode change - my original question, which to my pax eyes seems underplaying it a bit.