Repeat Ex. 30.21 if the common-mode voltage coming out of the op-amp sees an offset of 50 mV, i.e., it is 550 mV.
The differential input and output signals with this output common-mode offset look exactly like what is seen in Fig. 30.67. The single-ended output signals, Fig. 30.68, show the offset (the signals swing around 550 mV in Fig. 30.68). Clearly a common-mode offset in the op-amp output signals isn’t a concern (unless it’s so large that it limits the op-amp output swing range). Likewise an offset in the common-mode voltage of the input signals isn’t a concern (this comment is easy to verify with simulations). What is a concern, though, is the value of the voltages used for V_{_{C I+}} and V_{_{C I-}}.