These are pretty easy ones to date as they were only in production for about a year before the later version came along with the date at 9 o'clock to prevent it being partly obscured by the chrono second hand in its rest position.

The 1966 introduction date for the 45 Dato is one of the most corroborated we have of all the Carreras. The only hesitation I have in giving 1966 for yours with absolute confidence is that the serial number is very nearly 7000 higher than mine. Even so, the likelihood is 1966, with a lower possibility of it being 1967.

We do see some bigger jumps in serials early on, so it's possible that not all the numbers are being used in the mid- to late-60s, whereas throughout the 70s it looks a lot more like they're all being used up. Some manufacturers allocate ranges for a model based on expected production and the estimates aren't always right, so maybe we see that sort of effect too. A lot will depend on the size of the batch cases are manufactured in too.

The more serials we get, the better we can narrow it down and the more accurate we can be. At the moment we see a largish range for these early 45 Datos, while all the evidence points to a short production run that is a bit at odds with the range but we can expect (and hope) things to become clearer the larger the sample of data we have.