Please would anyone be able to shed some light on what this means ? Does this show the vehicle was specially built or is it a common thing ?

It can mean a number of things, it could be that the car went through LR workshops for an option to be fitted, it could be that its ex Royal Household. There used to be a department in JLR called "Traceability" that you could ring and quote your VIN and the Contract Number and they'd give you some info, so when it was built and why it was an SV.

Even though GDPR applies to people/personal information, they may refuse, I've had it with dealers over service history.

All of the P38 Autobiographys have that plate fitted.

Back then an Autobiography was uniquely built for each customer as per their specification, it wasn't a run of the mill spec from the brochure.

I believe the 2002 Vogue SE's with rear seat entertainment had it fitted as well.

David. 2002 4.6 Vogue SE - Alveston Red with Lightstone Leather
2007 Range Rover Supercharged in Java Black with Ivory Leather
2012 Range Rover 5.0 SC Autobiography in Indus Silver with Jet/Ivory Interior
2012 Range Rover 4.4 TDV8 Autobiography in Baltic Blue with Sand Interior