From what I recall reading in the book The Finished Mystery there were originally 4 or maybe 5 'classes'.
There were two heavenly classes, the 144,000 and the Great Multitude. The earthly classes included the non-Bible Students who survived Armageddon and two earthly classes including the resurrected Patriarchs (and Israelites) along with a general earthly resurrection. This was Charles Russell's doctrine. Don't know when it was all changed though but it appears that Joseph Rutherford did all the revision/simplification starting after Russell passed away.