Thx for your summary and your questions. One point to consider, namely your query,
then what exactly is the point of the preaching work?
they have long taught that saving via the preaching work is not the primary purpose of it. It is first to make God's name Jehovah known. In this they have succeeded. I remember when I was out in the FS people used to say things like, "Oh, it's you Jehovahs again." I got so tired of it I almost told one householder. Yep, I'm Jehovah God. I've come down personally from heaven just to speak with you!" If I recall, I was being harassed some Machiavellian elder that day, so I was not in a good mood. But you've got to hand one thing to the org: they have made the name "Jehovah" known in a lot of places.
Perhaps the AM part here was partly to deal with the fact that the whole earth has not come to know this name, like in China, much of India, and most Arab lands (?).