First, nobody can "prove" the inspection happened. The GB simply strings a few prophecies together and declares that it happened. Here is a typical explanation from the Watchtower;
*** w93 5/1 pp. 15-17 Expanded Activities During Christ’s Presence ***
Expanded Activities During Christ’s Presence
“Then the king will say to those on his right, ‘Come, you who have been blessed by my Father, inherit the kingdom prepared for you from the founding of the world.’”—MATTHEW 25:34.
CHRIST’S presence—the long-awaited event! The time like “the days of Noah,” which Jesus spoke of in connection with “the conclusion of the system of things,” arrived in the year 1914. (Matthew 24:3, 37) But what would Christ’s presence, or pa·rou·si´a, mean for the anointed remnant of “the faithful and discreet slave”? (Matthew 24:45) Why, that they would have to become increasingly more active as light bearers! Marvelous things were due to happen! An unprecedented gathering work was about to begin.
2 First, though, these anointed Christians needed cleansing. As Malachi 3:1-5 had foretold, Jehovah God and his “messenger of the covenant,” Jesus Christ, came to inspect the spiritual temple in the spring of 1918. Judgment was to begin with “the house of God.” (1 Peter 4:17) Malachi 3:3 foretold: “He [Jehovah] must sit as a refiner and cleanser of silver and must cleanse the sons of Levi; and he must clarify them like gold and like silver.” It was a period of refining and cleansing.
3 Passing through this judgment, which climaxed in 1918, the remnant of the slave class was cleansed from worldly and religious defilement. Why did Jehovah cleanse them? Because his spiritual temple was involved. This is the templelike arrangement for worshiping Jehovah on the basis of the propitiatory sacrifice of Jesus Christ. Jehovah wanted his temple to be in a clean condition so that when large numbers of worshipers with earthly hopes were brought there, they would find a place where his universal sovereignty is respected, where his divine name is sanctified, and where his righteous laws are obeyed. Thus, they would appreciate Jehovah and join in making known his grand purposes.
Added Privileges
4 In 1919 the cleansed slave class could look forward to ever-expanding activities. Back in 1914, Jesus Christ, their Master, had obtained a heavenly Kingdom. When he returned to his household staff to inspect all his “domestics,” he was arrayed in royal dignity, which he had not possessed when he was down here on earth. What did he find? Was the slave class busy caring for the Master’s interests? As recorded at Matthew 24:45-47, Jesus asked a question that challenged each anointed disciple to examine his personal devotion to Jehovah’s Messiah: “Who really is the faithful and discreet slave whom his master appointed over his domestics, to give them their food at the proper time? Happy is that slave if his master on arriving finds him doing so. Truly I say to you, He will appoint him over all his belongings.”
5 Obviously, Jesus’ description of this faithful slave does not fit any individual human. No, but it does describe Christ’s faithful anointed congregation as a whole, as a group. The domestics are Christ’s anointed followers as individuals. Jesus knew that he was going to purchase these anointed ones with his own blood, so he fittingly referred to them collectively as his slave. First Corinthians 7:23 says of them: “YOU [speaking collectively] were bought with a price; stop becoming slaves of men.” Jesus commissioned his slave class to let their light shine to attract and make other disciples and to feed his domestics progressively by giving them their spiritual food at the proper time.
6 From the time Christ’s presence began and down to 1918, the slave class, despite unpopularity, persecution, and even some confusion, had been seeking to give timely food to the domestics. This is what the Master found when his inspection began. The Lord Jesus was pleased, and in 1919 he pronounced that faithful approved slave class happy. What was the slave’s delightful reward for doing what his Master had appointed him to do? A promotion! Yes, larger responsibilities were given in advancing his Master’s interests. Since the Master was now a heavenly King, why, then, his earthly belongings became even more precious.
7 So, what are “all his belongings”? These are all the spiritual assets on earth that have become Christ’s property in connection with his authority as heavenly King. This definitely included the commission to make disciples of Christ, with the grand privilege of acting as representatives of God’s established Kingdom to all the nations of the world.
8 Such a promotion to oversight of all the Master’s belongings demanded that the slave class give more time and attention to getting the Kingdom work done and, yes, develop larger facilities for that work. It now had a much greater field of work—the entire inhabited earth."
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As illustrated by the above, they are simply interpreting scripture and fitting things together in a way that appears to give them the authority that they claim. If one accepts that they have the authority to do that, then it is the end of the matter as illustrated by the apologists for the WTBTS that we encounter here and elswhere on the net. However, it only takes a little critical thinking to see the flaws in their arguments. One of the posters here likes to quote Matt. 7:20 (The entire passage includes verses 15-20) "By their fruits you will know them." I tend to agree with him/her. If I could see by their actions that they really do follow the master, then I could put up with a few imperfections now and then. I don't think that I should hold folks to an impossible standard. After 30 years, though, I feel that their actions just don't back up the claims.
As to the lack of the FDS doctrine in the new "Knowledge" book, It is not that surprising to me. Notice that they moved it to the new "organization' book. In view of the rising number of people with a higher education in modern society, it's pretty obvious that they want to wait until they've already got people roped in before they spring that doctrine on them.
Just my opinion.
Forscher