1. User Guide
As it says in User Guide (UG) on page 16 of device :
“In case of an input error, the error code is written in the most significant byte of the corresponding AIn REAL register instead of the measured value.”
So for example...

Yes, every analogue input can be configured and used as a discrete one.

ADC resolution is 16 bit.

If the accuracy of the input or output of the module is no longer in accordance with the specification, it can be calibrated. Each analog input and output has its own calibration coefficients for each sensor type. – The calibration is performed us...