Intro To Level Design Tutorial --workflow question

Hello,

I was checking out the Level Design tutorial. I really liked it. I have a question about how Epic internally does their workflows in multiple passes. In the tutorial it’s stated that the blocking level is used by artists in the subsequent passes and if I understand correctly, changes to the game play are then able to be updated upstream in the more complex passes.

Does the internal team import the basic block geometry into Maya or 3DSMAXand build on top of it, or are new more complex meshes created and then the block level has it’s pieces replaced by in Unreal? In other words is it mesh by mesh or just one big export?

I realize there are a lot of different workflows, but I am curious as to how it works inside Epics team.