I'll agree that a 13 footer is rare to see, and rare to catch, but I believe there are plenty of huge gators never seen by man. Lake Monroe is very large.
Lake Jessup has its share of large gators as well. I remember when Lake Jessup was unknown to most people outside of Sanford. Now there is a bridge going over Lake Jessup and homes built around it. More large gators are bound to make an appearance (IMO).