In response to a question posted by Dan B., we’ve discovered that the WSFS Business Meeting members made instant-runoff voting (IRV) part of the Hugo Award process at NYcon III in 1967, and it was used for the first time on the 1968 Hugo Awards at Baycon. The Short History of the Hugo Awards Process page has been updated to reflect this new information.

Thanks to the people at FANAC.org who’ve been working hard at scanning and uploading historical fandom documents which make this sort of research possible, and to Dan B. for asking the question.