From the OP post,"You are able to claw back to finish 3rd in that race and go on to win the regatta nine points ahead of the 2nd place boat in a very large fleet."
How many very large fleets participated in the BBS? What is the point hit for DSQ, RET or DNF? Only two fleets had 1st place fleet winners that placed 3rd in the fourth race. Both fleet winners finished nine points ahead of the second place boat. One fleet had seven participants and one had 29.
In the seven boat fleet you are correct, they win either way....
In the "very large" 29 boat fleet they would not win. As far as i can tell they would place 5th if DSQ, DNF or RET.