usually it is considered that the input signals are within the stipulated CM range for the opamp, AND, that there is zero CM ac signal to contend with.
It is a whole different design matter if there is significant AC CM signal on the inputs, then, formulae for CM gain/attenuation need to be considered in determining what the real output will be,
as in many things the CMRR rolls off with increasing freq, hence more of any CM signal reaches Vout as the freq goes up ....