Do you know if there's a relationship between the Blaylocks and the Robinsons. A gift of a heifer was a fairly standard gift from a grandfather to a grandchild. Robinson's wife was named Elizabeth, so there's also a chance Elizabeth Blaylock was named for Jeremiah's wife. Anyway, there's some sort of close relationship, if only one of neighbors. You should try to get the full transcript. It will help place your family within a family or circle of associates. (I tried to find it online but couldn't.)
Your best bet for finding records for an early VA family is the court records. Men were VERY litigious in those days. There are abstracted Northampton Co court records as early as 1628. See books by Susie Ames and ?? Mihalyka. The St. Louis County library has the National Gen Society's collection which is available via ILL. The Mid-Continent Public Library lends books as well. I didn't check either catalog but hopefully you will find them. I order books this way all the time. They usually won't send out two related volumes at the same time (i.e., vols. 1 and 2), so order volumes from two different series. Sorry if I'm telling you what you already know. Just throwing out some ideas.