Those jaguarforums.com pdf links are very useful - the information is also on the JDHT XJ40 Supplementary model information DVD (JHN1130)
The XJ12 has the same interior specification level as the Jaguar Sovereign - in spec terms it is effectively a Sports pack Sovereign 6 litre.
Jaguar would make a car with pretty much any colour combination the customer ordered - they were very flexible, which is why the individual XJ40's specification varies so much. Oddly, the VIN 'plate' does not show the presence of contrast piping - the same interior colour code is used for piped and unpiped seats. Cars with a different carpet from usual will also go unrecorded on the VIN 'plate'. Both will be recorded on the car's factory build sheet, but they are closed in the archive now. My own car has Savile grey leather seats piped Isis blue. The code for that is ZLY - which is what is recorded on its build sheet. The car itself just displays LDY - Savile grey without contrast piping.
To demonstrate just how flexible Jaguar were, the seats on both of these cars were ordered new from a dealer like this by their first owner - and trimmed like this in the Jaguar factory when the car was first built. viewtopic.php?f=25&t=50&start=20