I think that "your" Andrew was an uncle of John M. Alexander. If so, then I think that Andrew sold some of his land in Bracken Cty. (then, it was still Mason Cty.) Kentucky to Archibald (Jr.). After Archibald died in Bracken ca. 1830, his widow, Isabella (Patton) Alexander continued to live there through the 1840 census.
Something (or someone) "drew" John M. to Missouri after the death of his father in 1830. I wonder if, somehow, David was involved in this. I see that david was in Adair in the 1840 census, but I also see a "David" of about the right ageliving in Bracken Cty., Ky. in the 1830 census. Could this be him?