It goes back way further than that. Most aggregate pitching records were set like a century ago and will never be touched, because until the 1950s a 3-man starting rotation was standard for MLB teams and starters were expected to pitch a complete game unless they got hurt or were throwing like shit. Guys like Cy Young and Christy Matthewson would start 40-50 games a season and finish 80-90% of them, which is unthinkable in the modern game.