The notion that TJ surgery itself increases velocity is a myth. You might see a post-TJ increase in velocity from your repaired arm compared to your injured arm. However, if when healthy you threw 90, you’ll probably still throw 90. If all goes well. You might have a slight post-TJ bump in velocity over your pre-injury arm, but that will be due to the year of extensive physical therapy and workouts, and won’t hold. See this, from two articles on TJ:
“Fit and rested, it’s no wonder that many feel better than they did and can often, at least for a time, show an increase in velocity and movement. In most cases, these gains don’t hold long. While Pitchf/x data does not go back far enough to give an extended sample, there does not appear to be a lasting change in velocity for someone who has come back from the surgery and rehab.”
"Two preliminary research projects have recently been conducted that looked at MLB pitchers velocity before and after having Tommy John Surgery. Rebecca Fishbein presented a report at the 2013 Sabermetrics meeting in Boston. She analyzed the average velocity of 44 MLB pitchers before and after undergoing Tommy John surgery between 2007 and 2011.
She reported no significant difference with velocity after surgery (she actually found a mild 0.875 mph decrease in velocity, though this was not significant). Stan Conte reported a similar finding at the 2014 ASMI Injuries in Baseball Course in 32 pitchers from 2007 to 2012. In Stan’s study, there again was no significant difference in velocity before and after surgery (he also found a 0.79 mph drop in velocity, but again not statistically significant).