Earlier quoted context omitted.
I might also be thinking wrong. But as far as I know, the puzzle doesn't explicitly prohibit this.
Yes it does. It tells you that a randomly selected prisoner will be taken to the switch room and allowed to turn one of the switches on or off...and will then be led back to his cell. There's no option for the prisoners to go to the switch room at the outset; they've just arrived at the prison and don't know where it is. So it would not be possible to meet up there, they have to wait for the prison guards to take the…
It says they can meet before doing to their cells.