The last I6 sedan was the 1997 X300, the last V12 sedan was the 1996 X305 (my father has one of these), yes.
To add to the reasons the leapers disappear, in the best Jaguar tradition the leaper will occasionally fall off the X300/308s when the tape disintegrates.
Also, some countries' dealership organizations/distributors will order their "stock" cars in a different spec; for example, we haven't had a manual Jaguar in the US (except for the X-Type) since the 1970s because Jaguar Cars North America thinks we don't want them.
Jaguar resale values drop like a stone thrown off a cliff.... a stone with giant rocket boosters strapped to it and a miniature black hole at the bottom of the cliff. Pre-X-Type, at least our resale values didn't have rocket boosters attached.... On the other hand, that's what makes them superb values when used. For the price of an econobox, you can have a large sport/luxury sedan.
$10K USD (what I paid for my car) would get me a stripper version of the Versa, the cheapest car in America or... my XJR. (Like that was a really hard decision...) $800 USD (which is what I paid for my Series III) wouldn't get me anything I'd want to be seen in.
Fantastic cars, fantastic values when used, but to be honest they're not for the average person and were never meant to be. If you want one and can afford it, give it a try. You may like it; careful - the big cats can be addictive.