That's all of them, Earl.
I'm sure I rode a 12 car train once, too. That was the very top end for a single 470.
The Private Cars were always run on the first train. They'd have to switch out a coach from the first train consist every time if there had been a Private Car run that day, because after '68, the first consist in on a given day was always the second consist out the next day. They'd just swing around the loop and go to track one or track two. I'm pretty sure I remember the daily switching would include adding the 11th car to trian one if there was no Private car.
So, you are right, there would have been no "extra" coach in the yard even if they ran a Private Car. That also explains why the number of available cars was what it was at 21. There was never any lost revenue with a chartered car in the daily consist.
Always, the bottom line.