The AI Modes do not correspond to different ground references, but rather just the configuration for the AI frontend. The EEPROM actually has more information than the device needs. Therefore, as you have mentioned only mode 0 is used, this is because the other modes are not used.
The AO mode also does not use all of the data in the EEPROM. In this case, unlike the third order polynomial fit that is used for AI, the AO is simply a linear fit. Therefore only the gain and offset are used.
Chris T. Applications Engineer National Instruments