I am also researching the Shorter family in Maryland. I am researching St. Mary's County and Charles County, Md.,both of which are south of Prince George's County. I do know how early descendents fled from my research area to D.C. once they were recognized as free people of color. There is a book about the Shorter family that may help you some. I do have bits and pieces on the D.C. Shorters that I have run across in my research though my family stayed in St. Mary's county until the present. My great grandmother was a Shorter.