First of all, thanks for the nice thread covering all aspects of this very nice JLC.
The first thing I would add is that some early models with solid case back were fitted with the old Cal.839. I do not know how many but the following TimeZone article from 2002 proves it:
http://www.timezone.com/2002/09/16/the-jaeger-le-coultre-master-ultra-thin/
The second point, another aspect and in addition to the technical marvel you described, is that the watch is not a museum piece to be left on a shelf. It is not only a technical achievement to show off how great manufaturer JLC is, it is also about mechanical performance: These watches have all been through the 1000hrs test and can be worn daily without any problem in term of accuracy. They are also 50m water-resistant, and according to the JLC owner's manual, you can swim (yes, swim!!) wearing it. I have not tried.
I love mine and tough one to the ones who do not appriciate them, that means more for me (the dream of owning them all is actually not impossible to fulfill, they are available and rather cheap)
Best,
E.