The Fiat 850 was introduced in 1964 and, in the Netherlands, from about October that year. I checked the sales lists of my father's dealership and the first Fiat 850 was delivered to the proud owner there on October 2, the registration was GL-06-32.
And from there I started counting and the following numbers are the result of a few hours work:
In 10 years a total of 1526 Fiat 850's was sold by my father; 32% of Fiat sales in the company! After the Fiat 127 and Seat 133 became available in the Netherlands sales of the 850 suffered.
The car dealership's building housed a stock of cars on the first floor, which could be reached via a homemade car lift. In the image you see that there were quite a few 850s in stock:
And the company advertised too; this one is from Autovisie: