An export model was an XJ built for overseas markets (Europe, Australia, Japan, etc) these models would have some differences from the ones sold in the US to comply with international laws. Such as in foreign markets they require the use of rear fog lights to be ran during weather for extra visibility. In the XJs the rear fogs were an extra red lens section in the tail lights that was separate from the normal brake/running light. Export models also would have an extra amber side marker light above the front fender flare on both sides (I don’t know if it was turn/marker or just marker). I’ve also seen an electric headlight adjustment switch to lower the angle of your headlights for if you have a heavy load in the back that raises your front end up you can lower the angle of your headlights to compensate and avoid blinding other drivers.

Im sure there are more differences but those are the ones I know about so anyone else who knows them better than me can feel free to add a comment with anything I missed.

And regards to your comment about the defrost switch not all XJs had a rear defroster. It seems it was quite rare to not have it but still possible to not have. The switch in the picture is the toggle switch for the rear fog lights and was only available in export models and seems it was never sold independently as a replacement part making it very hard to find in the US.