Auto promotion is determined by the top record across all leagues in a division, with PD as the tiebreaker. Each division has a certain number of auto promotion spots available each season (plus extras for bots but that is rare). There is 1 auto promo spot into NBBA, 4 into D2, and 16 into D3. In D2, having the best record across all 4 divisions guarantees you the auto-promo spot, which makes playoffs less stressful and allows you to shop the TL for NBBA caliber players before the craziness during the offseason. In reality though, auto-promotion goes to the team with the best record that does not win their league championship.