I remember seeing that 560 stated as the last to enter the UK - like you I can't believe there isn't a newer one than that.
On a general level, when the W140 came out in early 91 (on a late "H" plate") the backlash from existing W126 owners was fairly immense. As such Mercedes reluctantly carried on building the W126 in significant numbers until about November that year. I believe the last of the '91 build cars (not to be confused with the 38 cars built as a last hurrah in April 92) were all fairly similar in spec. In other words they're all pretty much identical to the one I've got as they weren't built to individual customer orders - that also explains why a number of them hung around the dealerships for a while & ended up on "K" plates. In essence, most of the late W126's are 500SEL's in blue black metallic, with orion grey leather, sun roof, air con, 15 hole alloys, front electric seats with driver memory, cruise, centre console rolltop box, no cat convertor and no air bags. The only regret is that when Mercedes were showering these cars with the catalogue options they didn't go for the heated front seats. That aside I think they got the look just about right & it certainly meant your average Captain of Industry or Megalomaniac dicatator needed to look no further for their chariot of choice.