What makes matters worse is that there's no discernible pattern here. The XJ, a full-size sedan (think Audi A8) is much larger than the XK (a diminutive grand-tourer à la the Audi A5), and slots in directly above its little sedan-brother, the XF (comparable to the Audi A4). Something the Germans do well (one of many things, admittedly) is plan: like addresses in a well-laid housing development, the numbers go up as you make your way through the line, but space is afforded between them in case a tougher-to-classify model has to slide in between.
BMW's 1 Series (teeny tiny), 3 Series (compact executive), 5 Series (mid-size), 7 Series (full-size luxury). When they built a large, two-door executive sports express, they called it the "6 Series." When they wanted a small roadster, they called it the "Z4." When they want to specify things like engine displacement, the taxonomy specifies gradations within a given line, like "328" or "335." You know a 335 is rear-wheel drive when it's called a "335i." Likewise, you know it's directing power to all four wheels when it's labeled "335xi."
When they build a crossover, even, you immediately know the specifics of the platform in relation to those initial, odd-numbered product lines. The X3 is a sport-utilified version of the 3 Series. If you want something racy, look for anything with an "M" in front of it. The M3 and M5 are salient examples.
All this is to say that BMW's nomenclature---while not exactly thrilling or evocative---serves a purpose, and serves it well.
Jaguar's nomenclature isn't only devoid of thrills or evocations, but it doesn't tell the consumer anything about the vehicle they want. I'm a connoisseur of these things, and I don't even really know what to call them. When I mention the XKRS to someone, I have to stop and think if I'm even talking about the right vehicle.
In the end, though, I can mostly forgive Jaguar for these marketing mishaps. They are currently putting out only three vehicles, and these three vehicles are truly among the best in each of their respective classes. I can't quite say the same for our next guest, unfortunately.
A comedy of grammars
Lincoln doesn't produce anything right now that competes with any of the big players in the entry-level luxury arena. They have, however, produced some visually striking vehicles over the last two years, and on this basis alone have entered my "cars I vaguely desire" list.
One of said vehicles resembles, for all intents and purposes, a sperm whale. It is called the "MKT" (I had to look that one up, FYI).