Yes, but it is also true that a lot of people never bother modifying their cars, aside from choosing their own specifications if they happen to buy the car brand new. A lot of the XJ40s' original owners were probably rich old farts who weren't into fiddling with cars (this is pure speculation of course). Of course the second hand owners may well have changed some of the features.

But with the XJ40s featured in movies, I get the impression in some cases they went for something cheap (that they didn't mind smashing up), so many of them could be older than the 1993+ cars (which is when the XJ12 was finally released). All XJ40s featured in movies made before 1993 (or was it 1992), are definetely XJ6s.