There are endless threads here about how great it would be if Amtrak would add and subtract cars when needed and how it is just not in their DNA and is also not a simple process. Hard to believe that has somehow changed for this train.
Especially since the train is being sold out.
I read not long ago an article in Trains Magazine that claimed Amtrak was doing just that. I thought at the time that it sure went against AU conventional wisdom.
There is a difference between adding cars for peak periods and taking them off for slow periods vs. adding an extra car to a train just because next Tuesday's run to California is almost sold out. That's an example, I didn't actually go check. Amtrak won't just add a car because sales on one day are going through the roof.
But again, they do add cars around major holidays and during other peak periods.