My IBM Selectric doesn't do "th" superscripts. And the typefact that looks like Times Roman has a straight apostrophe, not a curled one.
Almost every typewriter I've personally seen had superscript 'th' on a key, but the 'th' was stylized and slanted, not merely superscripted 'standard' font.
"My IBM Selectric doesn't do "th" superscripts. And the typefact that looks like Times Roman has a straight apostrophe, not a curled one."
I don't understand why people keep talking about the Selectric. That's out of the picture, since it doesn't have proportional spacing. What your Selectric ball has on it is irrelevant.
The only common machine that produced proportional typing at that time was the IBM Executive typewriter. Did it have curly apostrophe's? I can't remember.