Yes some are redrawn, In the past I have helped Diane sort out some of what gets sent in, Biro on lined A4 is a good example that can’t go straight into the mag. Mine just get reduced from A4 to allow two to a page.
The problem with you deciding how many parts is that it may not suit the page layout if the editor does not have room for what you put in one part or ends up with half a page. That is why I number from 1 through to the end then it does not matter where it goes.