historical question

[Magicbird]

Can somebody help me with a historical question?

I know that the NCAA went to a three-official system starting in the 1977-78 season.

But when did the college game go to two officials?

I have box scores from as early as 1938 that show two officials. But I have game stories from 1920 that indicate that just one official worked the game.

So obviously, the two-official setup happened after 1920 and before 1938. Was it a gradual change or was there a single rule change?

Thanks for any help on this subject.