I don't know P. Hickman's book or how she assembled her data, but I suspect it isn't complete. Here is a link to the official State of West Virginia's website for their project to digitize all marriage, birth and death records available. They're not finished yet, but some counties are getting there. Harrison is one of those with quite a bit of data online. If you haven't tried this search engine yet I strongly suggest it:http://www.wvculture.org/vrr/va_select.aspx
It has a flexible and powerful search engine, and positive results will link you to online copies of the original documents. This is probably a little off-topic for the Bath County discussion board, but it's a great resource if your ancestors moved back and forth over the border from VA to WVA.
BTW, I just went to that search engine and looked for surname=Ross in Harrison County in 1858 and got 2 results: Mary Ross and Nancy Jane Ross.