It has been said that the transformation of the Worldwide Church of God from Armstrongism to mainstream Evangelicalism was a unique event unprecedented in religion.
That is not true.
While appreciating that the transformation was an increditably traumatic experience for everyone involved and so it will always be remembered as an important part of their lives nevertheless the truth must be stated that this was not a unique occurrence. Remarkable it was. But there was other occasions.
Observe what happened to the Nation of Islam.
It was started up around 1930 in Detroit by Wallace Fard Muhammad. In 1934 he left Detroit and was succeeded by Elijah Muhammad who would lead the organization until his death in 1975.
Although they claimed to be Muslims the Nation of Islam under Elijah Muhammad taught many doctrines that contradicted orthodox Islam. Elijah Muhammad taught that Fard Muhammad was God, that God is a Black man, that Whites are products of a scientific experiment by a prehistoric "scientist" named Yacub and other such teachings.
Upon his death in 1975 Elijah Muhammad was succeeded by his seventh son Warith Deen Mohammed (1933-2008). Under his leadership the Nation of Islam came to abandon many of their distinctive doctrines and embraced orthodox Sunni Islam.
His transformation of the Nation of Islam was described by Joseph P. Gudel and Larry Duckworth in their article Hate Begotten of Hate (1986) under the heading, "Wallace Deen Muhammad":
[Warith Deen Mohammed] immediately began to root out some of the main tenets of the old Nation of Islam. He denounced the belief that Fard was an incarnation of God, a teaching which is anathema to orthodox Muslims (see Part One of this series, "Islam's Worldwide Revival," Forward, Fall 1985). Likewise, "doctrines defining God as black and dismissing whites as devils" were changed "with the explanation that the former ideas were necessary transitional beliefs because of the brain-washing the blacks underwent as slaves." [Footnote: "Islam and the American Blacks," The Link, Sept./Oct. 1979, 6.] Indeed, whites were now permitted to join their group. Since 1975 the movement has been accepted by orthodox Muslims as legitimately Islamic and one within the fold of Islam. [Footnote: ibid.]Like WCG the original Nation of Islam organization changed its name and is now named the American Society of Muslims.
However in the same way that WCG's transformation produced splinter groups determined to continue following the old ways the same thing happened with the Nation of Islam. Several splinter groups emerged. By far the most prominent is Louis Farrakhan's sect which has now taken the name of Nation of Islam for themselves. Similar to how some COG splinter groups cite HWA continuously, even reprint his articles and books, Farrakhan's Nation of Islam also reprint Elijah Muhammad's writings.
From Gudel and Duckworth again under the heading "Ideology" in the "Louis Abdul Farrakhan" section:
The ideology of the Nation of Islam under Farrakhan is almost indistinguishable from what it was under Elijah Muhammad. Their monthly paper, _The Final Call,_ reprints numerous articles of Elijah's writings and speeches. They also reprint Elijah's Muslim program ("What the Muslims Want" and "What the Muslims Believe") on the back page of each issue of the paper.So we see that WCG's "apostasy" was not a unique occurrence at all. It does not prove that Satan hates it any more than he hates the Nation of Islam, a religion that cannot be considered Christian. Therefore the Armstrongites have no right to view this as somehow confirming their legitimacy. Indeed whenever any mass exodus from WCG occurred some Armstrongites would always label it the Great Falling Away as xHWA exposed in his blog Great Falling Away?
Therefore the occurance of WCG's transformation was not a unique occurence.