1) A nation believes that they are God’s chosen people and rest of the world is pagan. When the history unfolds, the so-called chosen people go under occupation by the so-called pagans. From this theological crisis, a new theology of a messiah (who would restore everything) is evolved.
2) When the Messiah did arrive, no restoration took place; rather Messiah himself was murdered. From this evolved another teaching that it was God’s will that Messiah should be murdered by sinners so that sinners can seek forgiveness on the basis of such a death.
3) Even about specific subject you can see such evolution. For example, resurrection of Jesus. Mark was written first, and he’s hardly got anything about the resurrection; Matthew comes next with little more information; and then toward the end of the century we get Luke and John, and then and only then do we find stories about Jesus eating broiled fish, cooking breakfast by the shore, inviting Thomas to touch him, and so on..And finally book of Acts saying about 40-day works of resurrected Jesus
Since Bible itself sets the precedent for theological evolution, JWs would not have any problem in changing according to the time.