How many percentage of the doctrines of Brigham Young does the Church accept including the plurality of wives?
This sort of question is really impossible to answer. There are two reasons:
1) Counting Doctrines of Brigham Young
2) Counting Doctrines the Church accepts
1) Of all the things that Brigham Young actually said, what will you actually “number” as a separate doctrine? He was prophet longer than any other in this dispensation. And he was noted for being very prolific in his advice and counsel. So, how many things are you going to count? I don’t know if anyone has ever bothered with such an undertaking.
2) Of all the things that all general authorities have actually said, what will you actually “number” as a separate doctrine? And what about “official church publications”? There have been thousands of general authorities in this dispensation. And each one has given MUCH advice and counsel to millions of people in thousands of settings. So, how many things are you going to count? I don’t know if anyone has ever bothered with such an undertaking.
Percentage? One may as well decide what 0/0 equals.
We all know that even prophets are fallible men.
A prophet [is] a prophet only when he [is] acting as such. – Joseph Smith; HC: 5:265
If so, how do we know when he’s acting as a prophet?
“To this point runs a simple story my father told me as a boy, I do not know on what authority, but it illustrates the point. His story was that during the excitement incident to the coming of [Johnston’s] Army, Brother Brigham preached to the people in a morning meeting a sermon vibrant with defiance to the approaching army, and declaring an intention to oppose and drive them back. In the afternoon meeting he arose and said that Brigham Young had been talking in the morning, but the Lord was going to talk now. He then delivered an address, the tempo of which was the opposite from the morning talk. …
“… The Church will know by the testimony of the Holy Ghost in the body of the members, whether the brethren in voicing their views are ‘moved upon by the Holy Ghost’; and in due time that knowledge will be made manifest.”
— J Reuben Clark Jr.; Church Leaders’ Words, 10
I should also include that, while Elder Clark did hear this from his own father, who knew Brigham Young, Elder Clark could not verify that Pres. Young actually said/did this. But it serves to illustrate that when statements are taken out of context, it is difficult to tell exactly what happened or what was meant, or whether it was the Lord speaking, or just a man who happens to hold a prophetic calling.
In the end the rest of the question doesn’t matter. We have continual living prophets to continue to refine the words of past leaders of the Church to how we would perceive those words today in today’s context. And if the words as they are would be perfectly understood, then no clarification or emphasis is needed. If currently living prophets say things differently, that is an obvious correction to what was said in the past without any reason to necessarily reference the earlier quotes.
And the most important reason to not call any of it “doctrine” at all is the following:
The fundamental principles of our religion are the testimony of the Apostles and Prophets, concerning Jesus Christ, that He died, was buried, and rose again the third day, and ascended into heaven; and all other things which pertain to our religion are only appendages to it.
— Joseph Smith, Jr.: Teachings of Presidents of the Church: Joseph Smith(2007), 49.