I have a set of Kents on the car and was looking for a spare that im missing.

The ones I have on the car are 6x15x35, part No C41290 yet while at the parts wreckers looking at a few i noticed they had stamped 6x15x33 part No CAC (something).... this last number is the offset. 33 vs 35 and part part umbers are different.

Does anyone know when this change took place from 35 to 33? and why the part numbers are different.

This is actually not an XJS, but i think you XJS fellas will know more about the Kents than others.
My car is a 1973 XJ6 S1.

Peter