The ATP website hasn’t confirmed this yet - I think Mochizuki still has a chance to overtake Nardi next week at the Yokohama Challenger. If Nardi loses his next match and Mochizuki wins Kobe this week, there’ll only be a 3 point difference between them. Correct me if I’m wrong.
Decided to simulate these using the UTS ‘Hypothetical Matchup’ feature that allows for these exact conditions as variables
Using ‘Peak ELO Rating’ for Prime Nishikori provides the date August 15th 2016 as the result
Fritz - 71.2% chance of Nishikori win
Hurkacz - 69.0% (nice) chance of Nishikori win
Rune - 73.4% chance of Nishikori win
Zverev - 62.8% chance of Nishikori win
Tsitsipas - 68.6% chance of Nishikori win
Rublev - 65.3% chance of Nishikori win
Sinner - 47.4% chance of Nishikori win
Medvedev - 49.9% chance of Nishikori win
Alcaraz - 50.7% chance of Nishikori win
Djokovic - 26.9% chance of Nishikori win