I have seen the Watson paper and it contains post hoc speculation attempting to reconcile BY and the doctrine of eternal progression. But nothing that indicates that BY actually had two different beings in mind.
I disagree. For example....
Mother Eve was the daughter of Adam." [WWJ 7:152, Aug 31, 1873]
Adam who? Sr. or Jr.? Did BY teach that Adam married his daughter?
In addition, here is what Watson himself says in his paper...
If you believe that BY believes LDS doctrine and scripture, Adam cannot possibly be God the Father because God is a resurrected being who cannot die again and Adam dies.
And you can go down the list of doctrines that BY knew that preclude any type of Adam - God theory....
Adam is not God
Adam is subordinate to Jesus Christ
Adam is a son of God
etc. etc.
Another example. Journal of Discourses 1:50-51. Wilford Woodruff recorded it long hand it is it different. For example WW reports it as the Father comming into the garden with one of his wives until he was able to beget a tabernalce of (Adam). He also distinguishes between God and Adam (Jr) is a god, lowercase g.
B.E. Rich also reports from the same sermon..."
Jesus, our elder brother was begotten in the flesh by the same character, who talked with Adam in the Garden of Eden, and who is our Father in Heaven". Another clear distinction.
It is evidences like these that make me quite certain that both you and Jason glossed over the Watson argument without really studying it or taking it's objections to Adam God into account.