...that Adam personally possessed / knew this Plan?
Oh, yes, that's one of their teachings. After the Fall, Adam was taught the Plan and ordained to their Priesthood.
Adam and Eve were among our Father’s noblest children. In the spirit world Adam was called Michael the archangel (see
D&C 27:11;
Jude 1:9). He was chosen by our Heavenly Father to lead the righteous in the battle against Satan (see
Revelation 12:7–9). Adam and Eve were foreordained to become our first parents. The Lord promised Adam great blessings: “I have set thee to be at the head; a multitude of nations shall come of thee, and thou art a prince over them forever” (
D&C 107:55)...
Some people believe Adam and Eve committed a serious sin when they ate of the tree of knowledge of good and evil. However, latter-day scriptures help us understand that their Fall was a necessary step in the plan of life and a great blessing to all of us. Because of the Fall, we are blessed with physical bodies, the right to choose between good and evil, and the opportunity to gain eternal life. None of these privileges would have been ours had Adam and Eve remained in the garden.
After the Fall, Eve said, “Were it not for our transgression we never should have had seed [children], and never should have known good and evil, and the joy of our redemption, and the eternal life which God giveth unto all the obedient” (
Moses 5:11).
The prophet Lehi explained:
“And now, behold, if Adam had not transgressed he would not have fallen [been cut off from the presence of God], but he would have remained in the Garden of Eden. And all things which were created must have remained in the same state in which they were after they were created. …
“And they would have had no children; wherefore they would have remained in a state of innocence, having no joy, for they knew no misery; doing no good, for they knew no sin."
Gospel Principles Chapter 6: The Fall of Adam and Eve