On a related note, as I understand it, even if the race committee do see a boat miss a mark but that boat otherwise finishes OK (you can "finish" without sailing the course), they cannot do anything about it other than protest; which makes a lot of sense to me...
From RYA/USSA
Guidance to Appendix A "A5. Race committees are reminded that, in the absence of a SI to the contrary, they must give a finishing position to any boat that starts and finishes as defined. If the RC believes that a boat has not sailed the required course they must protest her (under the last sentence of rule A5 they cannot disqualify her without a hearing nor score her DNF)."
Regards,
Colin
www.sailwave.com