Actually, this is a reason why I had NOT been convinced that the documents were fake. I remember using IBM Selectric's with the "type balls" in the early '70s. Different type balls had different single stroke special characters. One of the keys on the typewriter would type various different characters depending upon which type ball you had inserted.
I don't specifically recall whether there was a type ball with a superscript "th" character, but I do remember balls with "1/2", "1/4", ©, ®, ™, and other special characters so there could very well have been ones with a single stroke superscript "th" character. If someone were using a typewriter with a "th" character they might very well forget to use it sometimes and type "th" instead.
However, the document overlay posted by Blood of Tyrants has me convinced. There is no question that the font on the "May 1972" document is identical to the font on the document that was just created by Blood of Tyrants.
I spent enough time manually preparing our school's newsmagazine, including service as an article typist relying upon an IBM Seletric that I can say I never saw a superscript 'th' on any of the various Selectric golf balls then available. My stint in this role is around the same time of these documents, and would apparently involve similar typewriting equipment.
"1/2", "1/4" are characters that even some other typewriters I used then, and some of those currently in my collection of same, include.
Why a superscript "th" but no "st" or "nd", for another example?
I further agree about the type itself; the Selectric is the only model of the time in my recollection that would allow for changeable fonts, and Times New Roman was not available until the advent of software word processing.