Am I right in understanding that the previous 737s 'stability augmentation systems', otherwise known as the STS, only ever used a speed signal, and that the innovation with the Max was the use of AOA in at least part of it? If so, I have a certain sympathy for the Boeing controls people since they seem to have tried to correct a basic mistake in the original system, to whit, using speed as a proxy for AOA. I count myself lucky in never having to fly the 737, only 75 and 767. The 757 had STS, copied I suspect from the earlier models, the 767 didn't. The result was that the 767 could be happily flown all the way down final approach with minimal input, while the 757 needed constant attention except in a complete flat calm. I don't think that excuses the lack of information in the AOM, though you can see why they may have thought the change in sensor would be transparent.