Rutherford's Kinemo films from the 1920s are featured in this video - in the one "The Great Pyramid" he shows charts saying 1925 was a key year.
The pyramid chart with the 1925 date comes on and off the screen from about minute 30 to minute 40 of this compilation (the video also has the Palestine and Imperial Valley reels included - Rutherford is in all three at one point or another.) Also there are more screenshots from "The Harp of God" published in 1921 (after "the faithful slave" was supposedly "appointed by God" and "out of Babylon" lol) where Watchtower was still teaching about 1799, 1874, and pyramids.