I replied with the following post to Linda as well. Hoping either of you might have something to share. As mentioned I have a photo you might like to take a look at.
My great-grandfather, Ideral King Van Fleet, married George-Ann Cosby in Hart County, Ky ca. 1860's-1870's. My g-grandfather became the first postmaster of Vanfleet, KY (later named Priceville).
I'm betting there is a connection here with your John Henry Cosby ca. 1840's. I especially find the postmaster connection interesting.
I have a photo of my g-grandfather and his new bride, George-Ann if you are interested. George-Ann died young, my g-grandfather re-married and I am a descendant of that second marriage. Would love to know anything about my g-grandfather or George-Ann.