1. Lexus usually shows an actual "concept" which previews some of the intended design but not the actual vehicle. Usually things are either very exaggerated or sometimes the concept previews design thoughts and not a particular vehicle.
I'll go a step further and say that Lexus will design the feasible, realistic production vehicle first, with all of the constraints imposed by stuff like platform/architecture hard points, providing enough interior space (especially headroom and legroom), crumple zones, etc.
Then, the designers will go back and come up with the idealized concept that reflects how they
wish the car had really looked like were it not for those constraints.
CT was the first time Lexus insiders admitted to me that this was sometimes their
modus operandi. In other words, the production CT was designed first, then came the LF-Ch Concept which is probably the way they really wished CT could've looked. Or perhaps the design process led to LF-Ch, then reality intervened with the constraints I listed above, plus European pedestrian safety rules, adequate suspension travel, and so on, leading to the production CT. Still, LF-Ch was unveiled 6 months ahead of CT 200h, even though it was put together after the production CT design was finalized.
I don't know if Krew or anyone else on here has heard one way or the other, but I strongly suspect the same thing happened with 5LS vs the LF-FC concept.
2. I think most are talking about the biggest change which was going away from the traditional doorline of the LS to one that adds the rear 3/4 window and D-Pillar.
Indeed, I strongly suspect this is the case. And seeing the LF-FC and 5LS pictures together in the post above shows what the main proportional differences are. The production greenhouse is taller and more ovoid, with more "ragged" and segmented elliptical shapes, versus the cleaner strokes of the concept. On the other hand, it's obvious that headroom would suffer big-time had the 5LS greenhouse hewed closely to LF-LC's. And Lexus does deserve mad props for the way it handled the side window/pillar transitions in such a flush and nearly seamless manner.
3. DO NOT expect every Lexus to look like the LC in regards to production from concept. The LC was not intended for production. Only after the RAVE RAVE reviews of the design and it winning every award in design did Lexus decide to build the exact same car. Contrarily the LF FC was a concept to showcase what was already coming in the LS... So the LS and LC initial concepts are from a totally different mind frame.
This cannot be emphasized enough. The LF-LC to production LC transition was unique in that regard. LF-Ch vs CT, and LF-FC to 5LS are more typical of Lexus' processes.