With gain settings of 20, 40, 80, 160V/V, an input amplitude of more than +/-50 mV, +/-25 mV, +/- 12.5 mV, +/-6.25mV respectively will cause ADC clipping.
The +/-32.5mV limit specified in the datasheet, is where the THD is less than 0.3% as listed in the EC Table Conditions column.
With a gain of 20V/V the input can go higher than +/-32.5mV and up to +/-50mV without ADC clipping but the distortion may be higher than 0.3%.
With gains of 40V/V and higher the THD condition is not the limiting factor because the ADC will clip before the THD condition.