This has happened before where an RO could identify 2 boats from a fleet that were NOT OCS but the rest of the fleet were.  The result stood.  
If I were RO It does seem unfair so if that many boats were going to be over, I would AP the start and reset.  

But, unless I am misreading the original post, the “restricted finish” in this case is 2/3 of the way up the course and nowhere near the starting area. The only boats playing in that area are the 18s and the H16s would only be there when finishing. So, again, I’ll ask, what issue are we trying to resolve by restricting this finish?

Agree.  As long as it's getting our of RRoS ok.

Draftable has a button to download the compared version.

RRS 63.5(a) requires protest committees to find facts 'based on the balance of probabilities (unless an applicable rule requires otherwise)'.

Finding fault of a boat’s own is a conclusion rather than a fact, so it's a matter fo  logical reasoning and judgemt by the protest committee, but, as fa  as it's relevant, I can't see any reason to depart from balance of probabilities.

Maybe it would help the discussion along if you pitched up a concrete example where you would be uncomfortable with BoP.