[Cboldt]

IBM typewriter with proportional spacing was introduced in 1941.

IBM announces the Electromatic Model 04 electric typewriter, featuring the revolutionary concept of proportional spacing. By assigning varied rather than uniform spacing to different sized characters, the Type 4 recreated the appearance of a printed page, an effect that was further enhanced by a typewriter ribbon innovation that produced clearer, sharper words on the page. The proportional spacing feature became a staple of the IBM Executive series typewriters.

http://www-1.ibm.com/ibm/history/history/year_1941.html

On the Executive, you could optionally have removable type-bars. This is somewhat like later Smith-Corona portables which have removable type-slugs on the two outermost type-bars, with corresponding changeable keytop caps. In this case, though, it's the whole type-bar.

http://www.geocities.com/wbd641/TypeManuals2.html

[Hank All-American]

If you will notice, I did not refer to proportional spacing as evidence of the spuriousness of the documents. It was the superscripting that I think is virtually conclusive.

[GoLightly]

Bwhahaha I used one that looked just like that one for awhile, but it must have been older, cuz it didn't do proportional spacing.

Superscript... at some point there was a lever to drop the carriage to do it & another lever to lift the carriage to do subscript. I was reminded of that after seeing pictures of typewriters today & one of them had a bunch of differnt levers above the keyboard.

I think the "Silver" we bought around 1980 or '81 had that feature, as well as a whole bunch of other bells & whistles.