I would suggest that depending on how one applies themselves, where they are in their own personal development (I doubt the Rocket would experience such a jump), yes you could improve velocity by a factor of that much using Tuff Cuff. I would say that a reasonable cross-section of under-classmen would have very noticable velocity improvement in that time frame.
It is a superior quality conditioning guide that is pitching specific and designed as a tracking log and isn't simply an exercise picture book, it has routine suggestions that are season specific..My sons High School coach got a copy from me..he put it into use the very next day and uses it to this day (My son has graduated).