>>281311089
I might have overstepped in my claims, not sure about Tezuka but here are pages indicating that Mizuki's friend and assistant Tsuge was sometimes responsible for layouts, visual direction, pencils, and inks, with the exception of the main character's rendering.
The Drawn and Quarterly Tsuge collections are great reads, not just for the manga, but also for the essays which are included giving background on the stories and the artist's life during each period.