Imerys and SACMI - Comparison, page-12

This is correct.

Giga and Uncle were saying you could just blend two kaolins and this will still give a white. As you said they can blend different minerals like feldspar, zircon etc into their kaolin which is what I have been saying. Imerys are not blending kaolins, the kaolin deposits they have are specific to the sanityware quality suited by chemical compositions with some added extra single minerals to get to their specifications.

You might find this interesting given you mentioned grolleg and also Iron oxide:

https://digitalfire.com/material/grolleg+kaolin