Before Joseph Smith
Before the dispensation of the fullness of times, were people taught such things as the 'Adam-God theory', 'Plural Marriage' and so forth? The nearest to Joseph's time would be just after the Resurrection. Were these things taught in the Book of Mormon? Were the Prophets then as thorough and detailed as Brigham and Joseph were?
I am sure that they did. First of all, there are the missing 40 day teachings of Jesus Christ. Second, there is the 2/3 to 3/4 of the Book of Mormon that is still sealed.
I don't think that the Nephites could have reached such a level of peace and righteousness as they did without having these Celestial principles and concepts taught to them.
Good question and any answer to it will be purely speculation because other than any secret meeting that took place even the BASIC doctrines were lost during the apostasy.