Caught a portion of this movie on TCM this weekend.
got me to thinking.
Release date for The Philadelphia Story: December 26, 1940.
And it would have been months before it reached movie theaters in smaller population centers.
I think it's safe to say that Katherine Hepburn as Tracy Lord got this particular name-game ball rolling.
As for the Jimmy Stewart character.
Macauley is not in the top 1000 names for any year of birth beginning with 1900. Please enter another name, sez the SSA Popular Names website.