Following along with Andy's point, this might help:
http://www.psacard.com/Articles/Arti...-1933-1947-era
And, here is the 21st home game that they played in 1954:
http://www.retrosheet.org/boxesetc/1...300NY11954.htm
The Giants were originally scheduled to play the Phillies on April 23, but the game didn't happen, it looks to have been made up with a doubleheader on April 25, so that May 30 game with the Dodgers was scheduled as the 21st home game, also.
Doug