(Wasn't the famous talk called, "Millions Now Living Will Never Die"? w09 8/15 p. 16 par. 17)
Do a search for "Millions Now Living" on the WT Library CD and you'll find a mix of "May" vs. "Will", with some references to "May" dating back to 1955 (the earliest I found was w55 4/18 p. 236).
The phrase "Millions Now Living May Never Die" appears 21 times on the CD. All are references to the famous talk.
The phrase "Millions Now Living Will Never Die" appears 194 times on the CD. Not all are in reference to the famous talk.
Interestingly, the Proclaimers book says there were two talks with different titles (but the same substance):
A footnote in the Proclaimers book on page 719 says:
1918 The discourse “The World Has Ended—Millions Now Living May Never Die” is first delivered, on February 24, in Los Angeles, California. On March 31, in Boston, Massachusetts, the talk is entitled “The World Has Ended—Millions Now Living Will Never Die”
Looks like Rutherford started having doubts sometime between February 24 and March 31, 1918!