We don't progress if we don't study and learn.
Disagreements should be settled as possible by facts. By evidence.
I'll ask Smith tomorrow about double heat treated parts and carbon migration. He's only heat treated a few Billion dollars worth of parts.
My guess at this time would be that for thicker parts, GM doesn't care. Samples are tested, accepted, rejected, or accepted and sent out for rework.
But I will definately find out.

A better discussion would be how to control colour pattern.

Out there doing it best I can.