From a reader (I’ve gotten many like it):

We still have an IBM selectric in the office. I powered it up and typed at bit.
The Letter Gothic ball has no smaller superscript “th”.
Interestingly, the repairman’s sticker and phone number was on the machine. I called, just now. He was working on one when I spoke to him. He said positively, no ball he has ever seen has had a “th” together. He said, too, that it can’t work as there are no keys on the typewriter with a “th”. I suggested the 1/4 or 1/2 (which is available) could have been a substitute key if the ball had a “th” or “st”, he said no.
He mentioned that NASA approached him, years ago, to see about symbology (math symbols etc.) balls that could work. He couldn’t help them with that.