Share 'Where does the Douglas sept of 'Douglass' originate'

For many years as a youngster, we were told that there was a tradition of adding or subtracting letters from a name when a child was born 'on the wrong side of the blanket'. I have yet to discover the significance of the second 'S' in my surname. can anyone help me. Perhaps there is a reason that even  with all the Douglas DNA  that is registered on file, to date, I have not even been close to a…