Daring post with all the no-date-PuristS among us: back in 1966 Heuer introducd the first Carrera model with date: the Carrera 3147 "Dato 45".
The "45" comes from the fact that the minute counter adds up to 45 minutes. The first generation "Dato" (like this one) were only produced in 1966 and 1967. It has to be assumed that the position of the date window at "12 o'clock" was rightly considered to be sub-optimal given the fact that the stop-second hand would most of the time be in resting position going over the date window.
The second execution "Datos" had therefore the date window at the "9 o'clock" position at the cost of the running-second sub-dial which had to go.
These Carreras were powered by a landeron 189.
Cheers, HSTE