Conclusive proof that the Selectric didn't do superscript can be found by looking at the papers of the designers of the typerwriter. They are available on the IMB website. The list of available letters is on the second page. No superscript "th" is available. Fogeries.
http://www.research.ibm.com/journal/rd/121/ibmrd1201E.pdf
IMB=IBM (too fast on the keyboard today).
IBM Executive (Models A - D) - proportional font, moving carriage, not certain what keyboard layouts were offered.
I find it plausible that superscript "th" and superscript "st" would be offered on a typewriter.