MLB extra inning information for regular season games exists here from the 1911 season forward (except for 1912). Thanks to retrosheet.org for the majority of the info. All playoff games have the number of extra innings listed.
College basketball before 1979-80 only includes the NCAA Tournament games, and overtime games are complete only back through the 2003-04 season.
The NBA neutral games don't match the neutral game won-loss records found in Sporting News NBA guides.
These are being annotated here.