Marty,
The Intro to Div 1 uses the single digit U, but it sure doesn't go to 70. And the format change might be a little earlier than 68. Section I adapted its current triple digit chapter heading format in 65 based upon the then existent format in Section VIII.
Of course, what the hell do I know. In the early 60's I was just realizing that girls weren't icky. Of course, 20 years later I discovered those were the ones I preferred.