There is no formula that produces a reliable percentage, and anyone who gives you a specific number is guessing. What can be said with confidence is what actually influences the outcome, and six years is enough time to build a genuinely strong case if he uses it intentionally.
Nevada's parole board looks at several factors when evaluating someone at a first appearance after a long sentence. Institutional record is the most visible and most controllable piece. An inmate who has gone years without disciplinary infractions, who has completed every program their counselor recommended, who has earned positive relationships with staff and demonstrated consistent pro-social behavior, walks into that hearing with the strongest possible file behind them. That file speaks before he says a word.
Programming completion matters specifically because it signals that the inmate took the time seriously rather than just waiting it out. Substance abuse treatment, educational attainment, vocational training, victim impact programs, whatever was recommended and available, completion of those things is what the board is looking for as evidence of genuine change rather than strategic compliance.
The interview itself carries real weight. Board members are experienced at reading the difference between someone who has genuinely reckoned with their offense and someone who is saying the right things. Preparation matters. His attorney or a reentry advocate can help him think through how to speak to the offense, the time he has served, and his plans for release in a way that is honest and credible rather than rehearsed.
The release plan also factors in. Confirmed stable housing, family support, and realistic employment prospects give the board a reason to feel confident that release is not a risk.
Six years is not a short window. Encourage him to treat every single one of those days as an investment in that hearing.