I was a secretary from 1966 to 1985 and went through many types and styles of typewriters from manuals to IBM selectric, to word processors to computer.
I worked for a lot of companies. I have never seen a typewriter of that era able to put "th" above the numbers.
Yes, we did do it manually by half-rolling the cylinder and typing lower-case t and then h and returning the cylinder to its position, but the t and the h would have been standard lower case letters and not the small version in the document.
PS. I also worked for the government.
Excellent point! I'd forgotten about having to roll the carriage up.