The Harp Of God was Judge Rutherford's first literary attempt at presenting his views. The book has gone through four seperate editions. The first edition came out in 1921, and is the only one that had the sub-title "Conclusive proof that millions now living will never die"
In the original edition, the premise was laid down that CT Russell in his person, fulfilled the role of the FDS here's what the book said: "Without a doubt, Pastor Russell filled the office for which the Lord provided and about which he spoke, and was therefore that wise and faithful servant, ministering to the household of faith meat in due season" [pg 239]
The second edition came out in 1928, and reflected a major doctrinal shift of monumental proportions. All reference to Russell being the FDS was excised from the revised edition. In the original edition pgs 235 - 241 were devoted to the subject of Russell and his special position in God's plan. This section was totally rewritten - pgs 240 - 248 - thus eliminating any suggestion of Russell's place in WTS theology. In fact in this edition, Russell's name deliberately does NOT appear. When the WTS quotes this book, THIS is the edition they quote from, giving the impression that they have always taught that the FDS is a class, not an individual.
Remember that the "Millions Now Living etc" slogan was designed for the year 1925, when it was expected that the "Ancient Worthies" would be resurrected. In anticipation of this the 1921 edition carried the slogan as a sub-title. All other editions being post 1925, naturally no longer carried this embarrasment
Two further editions came out, one in 1937, and the other in 1940. They contained no major change from the 1928 revision. However, there is one interesting historical footnote to the two later editions. In 1930 Rutherford formally changed the date for Christ's "invisible Parousia" from the original 1874 to 1914 [See The Golden Age magazine 1930, pg 503]
Now, the curious thing is this: These two newer editions for the Harp of God were still publishing, in 1937, and 1940, the old date!! Imagine the confusion among the R&F members. Here they were told in 1930 that the new date was 1914, yet publications were coming out in 1937 and 1940, respectively, using the old date. Obviously, the proofreading or editing was not as controlled then as it is now. The dates slipped through. Methinks the WT "god" was asleep at the wheel.