I doubt the Watchtower will answer your question directly, they are not going to admit "we change doctrine, making our disfellowshipping process invalid in certain situations" particularly since they say God's spirit directs the disfellowship process. If you look at the following quotes, it strongly shows that a disfellowshipped person had a gross, wrong, unrepentant attitude. It is considered inappropriate to "leave Jehovah" over a simple doctrinal error, particularly since the Organization primes followers to accept that the light will always get brighter. (What a double tongued organization)
*** w06 11/15 pp. 27-28 par. 9 Always Accept Jehovah’s Discipline ***
Repentance is a very important factor in connection with reinstatement into the Christian congregation. A disfellowshipped person is not automatically accepted back into the congregation after a certain amount of time has passed. Before he can be reinstated, his heart condition must undergo a great change. He must come to realize the gravity of his sin and the reproach he brought upon Jehovah and the congregation. The sinner must repent, pray earnestly for forgiveness, and conform to God’s righteous requirements. When requesting reinstatement, he should be able to give evidence that he has repented and is producing “works that befit repentance.”—Acts 26:20.
*** w06 11/15 p. 27 par. 3 Always Accept Jehovah’s Discipline ***
Disfellowshipping takes place only if a member of the congregation unrepentantly engages in gross sin.
*** w63 8/1 pp. 472-473 Proper Viewpoint of Discipline ***
Reinstatement is not just a matter of waiting for a specified time to elapse and then making the proper request in writing to the congregation. No; during the period of excommunication the wrongdoer’s heart condition, his basic attitude, must undergo a profound change. The sinner must fully realize the gravity of his wicked course and the great reproach he has brought upon Jehovah and his organization. He must feel cut to the heart. But he must do more. He must go farther than mere recognition of a wrong and feeling sorry. He must repent, which means to feel such sorrow for sin or fault as to be disposed to change one’s life for the better. There has to be a converting or changing of his entire course of action. Yes, he must “set matters straight” in harmony with God’s righteous requirements. Then he can approach the congregation committee, acknowledge his wrong, and give evidence he is living a clean life and will continue to do so. In this way he will prove that he is worthy of receiving Jehovah’s undeserved kindness and be reinstated.
*** w85 7/15 pp. 30-31 Questions From Readers ***The Aid book adds: “Among the varied causes of apostasy set forth in apostolic warnings were: lack of faith (Heb. 3:12), lack of endurance in the face of persecution (Heb. 10:32-39), abandonment of right moral standards (2 Pet. 2:15-22), the heeding of the ‘counterfeit words’ of false teachers and ‘misleading inspired utterances’ ( . . . 1 Tim. 4:1-3) . . . Such ones willfully abandoning the Christian congregation thereby become part of the ‘antichrist.’ (1 John 2:18, 19)”