Before we start as few words on proportional spacing.    It was invented in 1941 and was included on the IBM Selectric 1 that was put on the market in 1961.    ( For a source look up Wikipedia Selectric 1 ).   

If you are given two documents and wish to separate the computer generated one from the typewriter generated one  almost all the characters will be identical.    But there two exceptions.    They are the double quote and the single quote characters.  

 Computers store font  information in memory and use two different symbols for opening a double quote and closing a double quote.    They  also use two different symbols for opening a single quote and closing a single quote.    The symbol used to close a single quote  is also used as an apostrophe.

Here is an example of computer generated quotes.   

Typewriters limit the number of characters they can print so they use one character for both open and closing double quotes.    They also use one character for the opening and closing single quotes and as above they use this character for the apostrophe.   The symbols they use  are either 2 vertical lines or one vertical line.

 This is shown in the following photo

Also important is the space required for the apostrophe is larger in typewriter text than in computer text. 

A close look at the so called "Killian letter" reviles that the apostrophe used is different in the two letters compared.     It is vertical in one letter and slanted in the other letter.   

here is a link to  the killian letter

Clearly the vertical apostrophe is a typewriter symbol and the other apostrophe is a computer symbol.    This is difficult to see but it is possible with a magnifying glass.   

As for the raised th in the text  it was possible to get custom "character sets on the IBM Selectric 1 that had custom characters.   

And here is another view of computer generated fonts.