Does each oxygen sensor spot need a separate calibration, or are the calibration values valid for the complete sensor spot batch?

In case all the sensors which you have on site are from the same batch it is sufficient to calibrate just one of them (or two - one for cal0 and one for cal2nd). It is not necessary to calibrate each sensor separately. Please find further information regarding the spot calibration in the sensor spot manual IM_SP-PSt3_PSt6.