It is correct about beginners training everday. Vince felt that they (beginners) had the drive, excitement, and fresh recovery abilities that allowed such punishment.
Once a trainee was more "advanced" there was no set training frequency - it was as varied as the workouts. The days of the week are arbitrary to the body, and I can't recall any workouts that were set to a fixed frequency. So frequency of training depended on your recovery abilities, passion, and progress.
I specifically remember Nick barking at me because I was having a bad day (the kind were everything feels heavy) and accused me of having overtonis. He literally kicked me out and called my dad to come pick me up. I didn't go back for a little less than a week.
At Vince's constant improvement was just expected. I guess they (Vince and Nick) figured that since you started training as much as possible until progress slowed - then logically you should begin limiting the frequency to allow full recovery and growth to take place as you improve. Since you mentioned you are drug free, I will mention that Nick often scolded me for my desire to train like the pro's - basically stating that the drugs significantly improved their recovery abilities.