It does not seem so simple, seeing the discussion on the Wikipedia page:
https://en.wikipedia.org/wiki/Talk:Vickers-Armstrongs
At some point the company name changed then, it seems, originally it has no final S then?

The manufacturer Vickers-Armstrongs https://www.imcdb.org/vehicles_make-Vickers-Armstrong.html is spelled incorrectly as "Vickers-Armstrong" without the S on the end. That is a common mistake, but "Armstrongs" is the correct spelling.

Ooops this might get messier than anticipated. Full list of XJS codes (deep breath ...) from ARonline is:

XJ27 XJ-S Coupe
XJ28 XJ-S Convertible
XJ41 F-type Coupe
XJ42 F-type Cabriolet
XJ57 XJ-S six-cylinder Coupe
XJ58 XJ-S six-cylinder Cabriolet
XJ63 XJ57 with projected Getrag manual gearbox
XJ71 XJ-S mules for XJ41 development programme
XJ77 XJ-S V12 Convertible
XJ78 XJ-S AJ6 Convertible
XJ79 4WD XJ-S
XJ87 facelift V12 XJS Coupe
XJ88 facelift AJ6 XJS Coupe
XJ89 facelift XJS Cabriolet
XJ97 facelift V12 XJS Convertible
XJ98 facelift V12 AJ6 Coupe

.. which has several dead-ends, non-production experiments, and too many things which are visually indistinguishable, so it's unusable for our needs.

XJ77 was the 1988+ V12 full convertible, which we've stretched by usage to include the subsequent AJ6 4.0 version launched with the 91+ facelift - fair enough, it gives us an identifiable collection for non-coupes. Splitting off the 4.0 wouldn't work in practice - the only clue is the bigger bonnet hump for the smaller engine, but Jag started putting the bigger hump on the V12s as part of the 91+ facelift, which means it becomes a dating attribute across all convertibles, not an engine marker. So all full factory convertibles being XJ77 is all we can do. And its mirror for same reasons of all coupes being XJ27 is similarly practical. The American Hess & Eisenhardt convertible conversions of XJ27 coupes predate factory XJ77, so XJ27 works fine for these without change.

XJ28 convertible in the above list was pre-prodction 1970s code for abandoned experimental/prototype only, but may have been revived for 1985+ V12 SC targa (see below).

XJ57/58. These are the two 3.6 six cylinder twins launched Aug 83, but not the 4.0 AJ6 sequels. Hopeless task to try to incorporate XJ57 for the coupe, as the humped bonnet is the only visual clue and it's difficult to use in practice when visible - I've tried, with some results but not enough to fully trust. And then all versions get it .. XJ58 was only used on the 3.6 SC targa convertibles (there were no 4.0 SC/targas), but digging deeper I discovered there were V12 SCs as well (July 85+) so although SCs are distinctly identifiable they're difficult to split (only that bonnet again), and there's no distinct code in that list which securely says V12 SC (unless it was revived for the V12 SC which is unproven and nobody ever uses it).

Summary - stick to what we've got, and abandon XJ58 idea - it's not reliable enough.

On the bright side, we (fingers crossed) seem to have successfully incorporated the stupidly trivial 1991 name change from XJ-S to XJS across everything.

On Wikipedia XJ57 & 58 are for the XJ-S with 3.6 litre engine: https://en.wikipedia.org/wiki/Jaguar_XJ#XJ_numbering_of_cars_and_engines
Which maybe matches the XJ-SC too... but these are then not the only ones to use that code?

About the XJ-S, what is the difference between XJ27 and XJ77? I don't see a pattern of why some use the former or the latter, but I only find references to XJ27 on internet.

I believe after 2012 they are all UK built. We have a few 2011s in the database, 2 I found and posted on that page, that are Japanese built.

I think from references in my Jag XJS bible by James Taylor - who usually knows his stuff - that the short-lived (84-88) XJ-SC targa-roofed convertible was uniquely coded [XJ58]. It was replaced by the full convertible in early 88, which is a different kettle of fish.

Have invited comments here, so pending any dissent, can this join the queue for a block update??

I don’t remember well, but if the few Japanese builds were early 2010/2011 ones, we could mark all 2012+ ones as UK-built? I don’t think any Japan-built post-facelift ones was found?
Out of curiosity I checked a couple of Italian press cars and they were both UK-built (plates EF911KS and EF864KY, respectively November 2010 and January 2011).

That might explain my surprise that apparently no-one had realised a huge dollop of F15s were made by Mackems (the native name for Sunderland folk). Looks like over-correcting??

I believe when @dhill_cb7 went through Jukes found out that there were a few early ones imported from Japan. However I think all facelifted ones were built in UK.
Agree on second gen, I believe they’re already marked as built in UK?

Nissan Jukes:
- as far as I can tell all 1st gen [F15] for UK, Europe, NZ and Aus were made in Sunderland, Englandshire. All other markets supplied from J, except for Indonesia which supplied themselves and Thailand.
- 2nd gen [F16] only built in Sunderland, again for UK, Europe, NZ and Aus. Not made in J or sold elsewhere - they all got different replacements.

But I'm only going from what wiki says - other confirmation would be useful.