A good rule of thumb is: Capacity = Length x Beam / 15.
If the NHMP observes a 20’ boat with more than 10 people on it, they will probably be stopped and checked.
Now if a citation is given fighting this in court could be interesting. It really depends on the size of the people. If the vessel’s capacity is 11 people or 1650lbs and you had 11 Dallas Cowboy Cheerleaders, they would be below the weight capacity. But then again, if there were 11 Dallas Cowboy Cheerleaders in a boat, they wouldn’t get a ticket in the first place.