USA Today’s PDF compilation of Bush’s official TANG records provides two examples in which the letters “th” were typed as a superscript (sorry, I don’t know how to format a superscript in the First Draft environment). Click the link and follow along.
On page three of the PDF, Bush’s Chronological Listing of Service, check out line two:
Pilot Trainee, 111th Fighter Interceptor Squadron, Ellingotn AFB, Texas (TexANG)
The “th” in “111th” is a superscript.
On page 10 of the PDF, in Bush’s Record of Military Status of Registrant, look at item 8:
Organization: 147th Ftr Grp
Once again, the “th” in “147th” is a superscript.
This IBM advertisement (via the Newsroom) proves that proportional type has been available since the 1950s.