Earlier I had written about the last time rained out games had to be made up after the end of the regular season.
I've been looking for more, but it's a rare occurrence.
Back in 1973, there were two rained out games made up on Monday, October 1 to help settle the NL East. The Mets had to win at least one of two scheduled games in a doubleheader at Wrigley Field to avoid a tiebreaker playoff. The Pirates played the Padres that day and needed to win that game and have the Mets get swept and force a three-way playoff among the Mets, Pirates, and Cardinals. They all would have been 81-81.
A whopping crowd of 1913 packed Wrigley Field to see the Mets win the first game 6-4 rendering all the other events of the day moot. The Pirates lost at home to the Padres before 2572 fans at Three Rivers Stadium.
Althought it wasn't a makeup for a rainout, the Cubs and Giants had to replay a tied game after the end of the regular season back in 1908. That was the makeup for the infamous "Fred Merkle" game of September 23, 1908, which went into the books as a 1-1 tie. The game was to be replayed only if it affected the championship. And on October 8, the Cubs and Giants were both 98-55. The Pirates were 98-56, but out of it. The Cubs wont that game 4-2.
In the American League in 1908, Detroit beat Cleveland by 1/2 game in the standings because American League practice did not require all rained out games to be made up. And when the season ended, Detroit was 90-63 and Cleveland was 90-64.