From https://www.mlb.com/news/faq-negro-leagues-stats-major-league-record
As for career leaderboards, the current standard for career MLB leaders is 5,000 at-bats and 2,000 innings pitched, which roughly equates to 10 full qualifying seasons (5,020 at-bats and 1,620 innings). Therefore, for Negro Leagues players, this standard has been set at 1,800 at-bats and 600 innings -- roughly the equivalent of 10 seasons’ worth of 60-game seasons.
This is f***ing dumb overall, but MLB has plenty of issues like Bonds, Arod and others not being in the HoF. So this is par for the course.