In the current MLB divisional breakdown, there are 6 divisions of 5 teams each, organized into two leagues of 15. As a result, interleague play is mandatory in order to finish the schedule in a reasonable timeframe! Otherwise two teams would always have half of a week off at a time, and you'd have to add a few weeks to the schedule.
This changed in 2013, ...
No, there is no "winning" record in the event file. That is what the Game file is for. I don't think there's a better way using the event file than to match the winning pitcher (which is easy enough to do), but the truly best way is to use the correct file for the correct information.
In the NBA:
2020: John Wall (2010 R1 P1) for Russell Westbrook (2009 R1 P4)
2019: Chris Paul (2005 R1 P4) for Russell Westbrook (2009 R1 P4)
2018: Blake Griffin (2009 R1 P1) for Avery Bradley (2010 R1 P19), Tobias Harris (2011 R1 P19)
2017: Kyrie Irving (2011 R1 P1) for Ante Žižić (2016 R1 P23)
2014: Kevin Love (2008 R1 P5) for Andrew Wiggins (2014 R1 P1), ...