Note that in every instance in which the 'th' following a number appears in superscript there is no intervening space between number and suffix.

MS Word is set to automatically substitute the superscript when you hit the space bar, but if there is an intervening space, the rule is not triggered, which would explain the lack of superscript in this document.

Instead, depending on the program's settings, you'll either get a normal 'th' marked for a spelling error, or an auto-correction to 'the,' which is easily corrected.

Why would the writer, even if a variable-width type head with a special supercript character had been in use, choose to use the superscript in one place but not another? My initial thought was that the superscript 'th' could be a convention in the naming of units as opposed to designating normal ordinals (the 147^th vs. my 5th cup of coffee).

But there's no consistency, and the facts weigh against undocumented documents.