Two classes for salvation didn't come from Rutherford. Russell believed there were three classes of saved: the 144K, a secondary spiritual class not quite reaching faith required of the 144K, and those who inherited a paradise earth.
Current Witness doctrine derives from earlier 19th Century sources, among them an Anglican writer, Isidore Heath, who wrote The Future Human Kingdom of Christ. This book influenced Henry Dunn. I don't know that Russell read Heath's book, but he read much of Dunn's material as republished by Storrs. None of the heavenly/earthly class teaching came from Rutherford. What he did was to eliminate the thought that there was a secondary, less faithful, heavenly class.
The Separate Identity series [2 vols. so far] considers the origins of Watchtower theology in considerable detail.
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