The Spartan-6 IBIS file does not contain models for the LVDS inputs on the "left/right" side of the device. This causes theIBISWriter to issue the following warning:
"WARNING:PostProcessors - IBIS model LVDS_33_LR_33 for I/O port <pin name> (pin<pin number>) could not be found. This signal will be listed as a no connect (NC) in the output file."
The reason for this is that LVDS outputs are not supported in the "left/right" region of the device.
That is why there is no data for those standards in the IBIS file, however,LVDS inputs are supported in the left/right regions.