The first proportionally spaced typewriter was released in 1941 by IBM.
From the IBM History page:
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.
Thanks. See post # 156.
Please read reply #198, and tell us if you think that was likely in 1972 in the TANG.