Ignition system ceramic resistor change point.

[MIG Wielder]

Hello All,
I'm aware that early 1850's ( before 9875 chassis number ) had the ignition coil ballast resistor externally mounted on the coil.
Later ones like SWK the ballast resistor was a piece of resistance wire built into the loom.
I've been reading the parts books.... Two of them; one for the early 1850's and one for all later Dolomites and its looks like ...

* No Sprints were ever fitted with the external ceramic ballast resistor. Is that so ????
* Only 1850's were ever fitted with that ceramic external ballast ? No record on early 1500's or 1300's ???

If this external ceramic ballast was fitted to early models what was the change point please ?

I do appreciate that the parts books and workshop manuals only told some of the truth ...

Thanks ,
Tony.