The question is...how many from the field?
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That's the $64,000 question.
In my 40+ years as a JW, whenever a speaker from the platform asked the cong. by a show of hands how many came in to "the Truth" from D to D witnessing, the result was always the same: most likely: 0; or, maybe one or two out of a cong. of 150 publishers. The vast majority were relatives/children of JWs.
The fact is most who become JWs, who aren't children of JWs, learn of the religion in the same way that every other religion gets converts: they learn about it through a workmate, a person in the religion that befriends the person, or through heresay. Very few actually convert as a direct result of the public witnessing, which makes the focus on D to D work even more ridiculous.