After you posted, I sent an email to Tim Huff of General Mills, with whom I have had many exchanges in the past, and asked him if he knew when high-gluten flour was first used for the NY style and, if he knew, whose flour it was. Apparently, this is not a subject of great interest at GM since he replied today that he checked around and could not find an answer.
Some time ago, I used the Google news archive search feature (since discontinued) in an attempt to find old articles in which the use of high-gluten flour was described for making pizza dough. I found some references to use of such flour for bagels and some breads but very few for pizza. My recollection is that it was perhaps in the 1970s that pizza operators started to play around with high-gluten flour for pizza and such use started to creep into articles on the subject.
I also took a look at Evelyne Slomon's book, The Pizza Book, to see what she said about the flours used at the time her book was published in August, 1984. I suspect that what she said in her book about flours reached back a few years as she was researching and writing the book. In her book, in the Flour section, she discussed all-purpose flour and bread flour. However, her description of bread flour was a bit fuzzy since she said that bread flour was sometimes called high-gluten flour and she also mentioned a protein content for bread flour of approximately 14%. Quite possibly the lines between what we now know as bread flour and high-gluten flour were starting to become blurred.
Since old habits die hard, I suspect that the transition by NYC pizza operators to high-gluten flours from the all-purpose and bread flours did not happen overnight. I wouldn't be surprised if it took several years for the transition to take hold, and that the process was gradual and perhaps accelerated when consumers started to indicate their preference or fondness for the pizzas made with high-gluten flours. it is also possible that pizza operators saw something functionally better using high-gluten flour. like more taste, better kneading and handling qualities, etc. And maybe they could charge more for their pizzas as a result.