Some analysts detect a commonality in the tab settings ~ which isn't terribly critical, but it does mean the typewriters in question were used EXCLUSIVELY in this process.
Different things happen on different days and the forms went into and out of platens several times.
You can buy off on that or not but over the years I designed or redesigned over 1,000 federal government forms, all of which were put into use by the general public, or for specific government purposes.
To do that job successfully I had to imagine every single detail of normal use ~ and supplement that with on-site field observations of people using models of the form under design, or its predecessor(s).
Again you miss the point. There would be no MIX OF MATERIAL anywhere on the parts where the form would BE FILLED IN, aka typed information.
Go back and re-read the article again.
Commonality in the tab settings have nothing whatsoever to do with different sizes in the typeface or slant of the typeface.
Go back and re-read the article again.