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Sorry, the existing topic wouldn't let me attach an additional file, so I had to start a new one.
The Selectric Composer explanation is plausible, since it explains both the proportional spacing AND the general typewriter-sloppiness of the document. See the extracted pdf page, attached, for a better example of the latter. The nature of the document was such that it probably didn't rate professional typesetting but still something probably a bit better than a typewriter, though I can't say they did a very good job with it. The type-twice method sounds painful....
Thanks, I learned something new today.