Also, you asked about whether it would be wise to mention that modern Bible Student groups adhere more closely to what the WTS taught in 1918-19. I don't think it would add much to the conversation to bring this up. The JW response is that the light gets brighter and those Bible Students are stuck in the past. It would be a distraction and would likely lead off on a tangent.I guess the only reason I would ask this question is to show that the folks who are presently known as JWs were not exclusive to their beliefs/thinking at that time...
I would be inclined to ask why Jesus did not choose the Associated Bible Students (Pastoral Bible Institute). They were teaching everything the Watch Tower Society was in 1918, excepting the bizarre new doctrines found in The Finished Mystery and Millions Now Living Will Never Die! (e.g. the false prophecies regarding 1918, 1920 and 1925).