Dozy:
As I understood it, prior to Birgenair that option was not easily available. The AIR DATA switch was retrofitted afterwards.
You understood it wrong. On every 757/767, there is a row of five switches just outboard of each pilot's EFIS with NORM/ALT selections for IRU, A/P, ILS, EFIP and Air Data. The EFIP is the symbol generator for the EFIS. The ALT selection engages the third set of Autoland Critical items. Air Data is not Autoland Critical, so there are only two ADC.
Going back to my original question: "When was the last time an airliner was lost in flight test? There haven't been an A300, A310, A320, A340 or A380, have there? You have to go back to the 707 or BAC1-11.
You don't like the A vs. B comparison: how about A vs. Fokker?