BTW:
The change from "in our 20th century" to "in our day" was in the January 1, 1989 Watchtower. The printed magazine carried the former wording, but it had been changed to the latter when the bound volume was issued (and, of course, in the later CD-ROM).
The book that said explicitly that Armageddon would come in the 20th century was The Nations Shall Know That I Am Jehovah - How? (p. 216). Ironically, this was the book that also claimed prophetic status for the organization (e.g., p.58).