Great information Paolo, presented in a clear and orderly style as usual.
This exact topic was on the lunch table here in Copenhagen yesterday. We could not come to a firm conclusion and decided we were going to have to draw you in to explain the subtleties of the early Autavia's. Then i log in today and you're already on the topic - we must have been psychic ;-)
Gret night lume shot BTW - all the more impressive when we consider you were pulled out of bed for daddy duties. My sympathy for you loss of sleep (i'm in the same situation at the moment with my boy) & thankyou for the good detective work on the early Autavia's.
Cheers - Darren
-
-: Here i attached the side view for mk1 case and mk2 case:

: mk1
:

: mk2
:

: in the second the lugs are much thinner, so the cases are very
: different, not only for the back case,
: that has the gasket outside the screw in mk1 and inside the screw
: in mk2.

: Looking at some watches recently sold, i can say that the
: transition from one case to the other was not between 80000 and
: 90000 but between 60000 and 65000.

: This watch is doubtless a second-ex case, second-ex dial, and the
: serial is 64271:

:

:

:

:

: This is the only watch i've seen in the serial range 60000 - 84000
: so this period is still obscure to me...

: The transition between 2nd ex dial and 3rd ex dial should have
: happened to me between 85000 and 86000:
: the earliest watch with 3rd ex dial i've ever seen is 85342, while
: the last with 2nd ex dial is 85349