There appear to be three areas where Jemson is not that uncommon, the North East of England, Lancashire and Southend on Sea.
My uncle did some research of the family in Lancashire going back to the 17 hundreds.
Perhaps we may be able to link the groups together. I shall try to find the documents and post some early names.
If anyone wishes to use yo(your name)@jemson.net email address let me know. I have registered the domain and messages sent to this domain are forwarded automatically to your own email addrss.