Sorry for my naivety, but how does a company keep memory of the processes and oral knowledge if they don’t own the factory? Is everything specified enough in requirement documents and process sheets that “factory providers” have a clear guide to implement their factory?

And does that really save on CapEx given that Apple funds the construction anyway and secrecy is absolute as well?

This situation let's the contract between Apple and the fabricators be results based and Apple can focus on Apple things and the manufacturer has the burden of spending the factory budget and getting results.

This helps keep crisp lines of delineation between design and production. That is my understanding.

The processes that Apple is outsourcing are considered disposable as the technology changes. The oral traditions and cultural knowledge are in the software/hardward/design ideals.