When checking for a duplicate lead in YGL, there is certain criteria that YGL will look at in determining if it is a duplicate lead or not.
It will check the first name, last name, phone number (stripped of non-numerics), and scores thse based on similiarity. In addition to that 'score', the first three letters of the last name and the first two letters of the first name must be an exact match. The system will also check for an exact match of the email address.
In closing, click 'Yes' on the potential duplicate lead pop-up if you have determined that the lead is not a duplicate and you want to save the lead as a new lead.