I think they promoted any bots that won their playoffs, and then did the bot cleanup. A bot won my league's playoffs (IV.18) but are now in IV.27, so I assume they promoted to some league in III, and then were swapped with an active team from IV.27. Because there are a lot of empty leagues in USA IV, the extra promotions went fairly deep. There were 5 active teams in my league that were promoted to III, and a bot that finished 2nd that remained in my league.