According to paragraph 15 in Chapter 4 of the book Gods Kingdom Rules the time had come in 1931 for Jehovah to allow his Bible students to adopt his name.
15 By the dawn of the 1930’s, our brothers had acquired a proper view of the importance of God’s name, a clearer understanding of the work God had assigned them to do, and a deeper insight into the main issue to be settled. Now, Jehovah’s time had come to give his servants the honor of publicly bearing his name. To see how that came about, let us consider some past events.
Apparently Jehovah didn't mind them still using the cross or having a seemingly wrong date for Christ's parousia.