Assuming you're referring to [0], that's a statistical estimate of valid chess positions (based on clever methods of uniform position sampling + fast validity t

Assuming you're referring to [0], that's a statistical estimate of valid chess positions (based on clever methods of uniform position sampling + fast validity testing), not valid chess games (based on estimating branching factors for very long games). [0] https://github.com/tromp/ChessPositionRanking https://github.com/tromp/ChessPositionRanking