Ok to sum up the answer to my original question
The definition of a Guest rider is one invited to ride but isn't a DSC member but ideally a member of the motorcycle press.
Scoring riders are anybody who fancies racing in DD and joins the DSC at any point before they race
And how things change
http://www.ducatisportingclub.com/xm...8392#pid166916 titled
"what the rules on 'guesting' ?"