I doubt these composers hand their “sketches” (17 staves worth sounds pretty complete) off to an orchestrator and forget about it. Remember that A.S. conducts his own work and has a traveling studio upstairs at the recording studio for any last-minute changes. He likely also works with orchestrators he has worked with before and who know what he wants them to do.
If I write 4 horn parts on a single staff, for example, I think I can usually trust someone else to split them into individual parts. I imagine the process of “handing off” is not as cavalier as you may think.
I say this as one who has always done my own orchestrations.