An IBM Selectric II and a IBM Selectric Composer are not the same thing. The Selectric II was either on every secretary's desk, or she was trying to figure out how to get one on her desk, for all of the 1970s. The Selectric II was a great, rugged, reliable machine, but it could not do proportional fonts.
I have been in office environments for twenty five years, and I have never seen a IBM Selectric Composer, ever. This was a piece of specialty equipment, and was not in common use.
You're right. I got confused with multiple pages I was looking at.
I used a Selectric Composer in 1975 working for the City of Anchorage. It did do proportional spacing and superscripting but was hugely expensive. Also, it was used in conjunction with an MTST -- about the size of a VW Bug. Did the inputting on the MTST tapes, then schlepped the tapes to the Composer. Doubt that the military had these two monster machines in every office.