For example, if you have SSTL 2 Class II input pins in I/O bank 1 and they are all placed in the VREFB1N0 group, then the VREFB1N0 pin will need to be powered with 1.25V to support the SSTL 2 input standard. If the remaining VREFB1N[x] groups (if available for your device) do not have voltage referenced input pins, then the remaining VREFB1N[x] pins (if available for your device) can be used as I/O pins.
Dual purpose VREF pins when used as I/O pins are not shorted with other VREF pins in the same I/O bank. They are only shorted when used for VREF functionality.
If you are using multiple VREF groups within the same I/O bank, the VREF pins for each group must be connected to the same voltage level.
To understand I/O pin placement with respect to VREF groups, you can refer to the Quartus® II software Pin Planner or the device pin-out file.