As far as I can tell, the 1-12 (instead of 3-6-9-12) dials were part of a general revision across the board for the 1972 model year. As in cars, it's not impossible that some of these may have started appearing at the tail end of 1971, but from sales literature it certainly appears that it was intended for 1972.

In Carreras, the equivalent hands to this Autavia were only used for the first two part years of production of the second generation (i.e. 1969 and 1970), so in the normal course of things the twain shall never meet.

Now, Heuer's stock policy at the time seems to have been to use up as many of the existing components as possible before using new ones, even with a model change imminent (sensible economically, I can't see Marketing departments letting this go today). This has lead to the many transitional watches we see, making it hard to judge whether some of the watches ever left the factory like that or whether one or more components were swapped out later on, either in the normal course of servicing or, more shadily, to assemble a watch from parts.

More than a year is a long time for a watch still to be made from transitional parts in this instance. Certainly Carreras had stopped using these hands with numbers somewhere around the 18xxxx mark, and changes to one of the main models tended to go hand in hand (excuse the pun) with the others in this period. I imagine that this watch might have had the hands replaced with the earlier ones, for any of the reasons hands get replaced - lume falling out seems to be common, but the reason why would only be speculation.

Whatever the case with this example, they make a very handsome trio in the group photo, congratulations. I'm a sucker for things that are almost the same but not quite, really gets my collecting gene kicking in!