This comment from July WT 2016 implies that at least some had the “earthly hope” already in 1919. I’ll keep looking for something more explicit.
“Has this promise of unity come true in our time? Yes. Initially, the prophecy began to be fulfilled in 1919 when God’s people were gradually reorganized and reunited. Satan’s attempts to divide them permanently had been thwarted.
At that time, the majority of those reunited had the hope of becoming kings and priests in heaven with Jesus. (Rev 20:6) Symbolically, they were like the stick for Judah. However, as time progressed, more and more of those with an earthly hope started to join themselves to these spiritual Jews.”
w16 July p. 31