Except for a brief period when HiSilicon was still making leading edge SOCs, Apple has been the first customer on TSMC’s new process technology, and always with a custom process flavor. This is completely normal.
What's the evidence this is both true and matters to the original claim? In some sense all nodes will be derivative of the previous one, as they never reinvent the wheel completely.
The evidence is that I am a subject matter expert and there is a very big difference between a derivative (ie half) node and full node. If you want to learn more about full vs half nodes, I would start with google.
