I found something from the reasoning book that destroys this claim. Usually this comes after accusing the Watchtower Society of being a false prophet.
Notice what they themselves say on page 133:
Ability to perform “great signs,” or “miracles,” is not necessarily proof of a true prophet
Matt. 24:24: “False Christs and false prophets will arise and will give great signs [“miracles,” TEV] and wonders so as to mislead, if possible, even the chosen ones.”
2 Thess. 2:9, 10: “The lawless one’s presence is according to the operation of Satan with every powerful work and lying signs and portents and with every unrighteous deception for those who are perishing, as a retribution because they did not accept the love of the truth that they might be saved.”
So just because they are doing this work, and it seems like a great sign...that is not proof of a true prophet.