1870 census Upshur Co, TX lists three Hoover families, Jefferson 43, b IN, Abraham 48 b IN, and :
Hoover, John, 21, b TX
", Margaret 25, b TN
", George, 2, TX
", John, 5/12, b TX
", Lucinda, 15, b TX
", David, 12, b TX
Obviously Lucinda and and David are too old to be children of John and Margaret. I think this is your lost David. What is your source of "little" Lucinda also dying? And, what is your source for death dates for the couple and baby? Just playing Devil's Advocate.
Matching birth year, again I think this is your David on the 1880 census Hunt Co, TX:
Categories: Name; Relationship to head of household; Marital Status; Gender; Race; Age; Birthplace; Occupation; Father's Birthplace; Mother's Birthplace.
David R. HOOVER Self M Male W 21 TX Farmer OH OH
Margarett HOOVER Wife M Female W 22 TX House Keeper TN AL
Sarah E. HOOVER Dau S Female W 3M TX TX TX
I would check the 1900 census for this David R. Hoover.
What Gate family supposedly took the young brothers? One on the 1870 in Colorado Co, TX, and is black. One named Gates on Upshur Co, TX, and is black.
Happy Hunting (^_^)