In the way you describe it, yes you may be able to use 12 single ended inputs.
But as in other threads already high-lighted, for the input specification and for best performance we recommend that all analog inputs are used in a range from AGND + 100mV to AVDD - 100mV.
So even in a single ended configuration we recommended to have a system common signal which is used for all other inputs as common reference. Counting that way, and having best performance in mind we only say 11 channels.