Yes, that's precisely what I mean by the tachys not being date diagnostic.

At launch in 1972, the Cal 15 Carreras are shown with tachy at 1:

and later on, as in the catalogue you show, they are still available with tachy at 3. So we can't use the tachy scale alone to place them in a date range. Nonetheless, as I said, in my experience you come across the tachy at 1 scale much more often on Cal 15 Carreras than the tachy at 3 one. That's not to say the latter is wrong, I also said they were used interchangeably; just that tachy at 3 is less common on them.