My understanding and belief is that the North American outpouring in the 20th century came through the Methodist holiness movement.
I tend to believe that at one time, most if not all, believed and obeyed the UPC manual out of conviction and because it was their conviction, tended to communicate that conviction to their saints as well.
Has it stayed that way among most if not all? Obviously not. But just as in the early rain after
Acts 2, Paul warning them night and days with tears about those on the outside who would come after he departed not sparing the flock and those on the inside who would rise up and speak perverse (distort, misinterpret, corrupt) things to draw away disciples after them; and those who would depart from the faith, etc. Peter and Jude also speaking of these types of people.
Therefore, there is nothing new under the sun. Just like in the early rain it happened, so now in the latter rain outpouring it is happening.
The apostolic organizations are shaking.
Heb 12:26 Whose voice then shook the earth: but now he hath promised, saying, Yet once more I shake not the earth only, but also heaven.
Heb 12:27 And this word, Yet once more, signifieth the removing of those things that are shaken, as of things that are made, that those things which cannot be shaken may remain.
Heb 12:28 Wherefore we receiving a kingdom which cannot be moved, let us have grace, whereby we may serve God acceptably with reverence and godly fear:
Heb 12:29 For our God is a consuming fire.