The judges who interpret the rule book are the authority. The casebook can provide those judges (and competitors) information from which to back up their position if they so choose.
I can see how this rule might be applied if you are both upwind or both downwind, but not if you are headed directly at each other. The rule specifically states "...a port-tack boat is keeping clear by sailing to pass astern of a starboard-tack boat...". You can't pass "astern" of a starboard tack boat when you are headed directly at each other.
This is a tough call and the ruling would undoubtedly be a judgment call where the judges would try to shake the facts out of the two points of view (and if you think your two points of view are 'strange'...it's not at all...it's rather typical).
Look at the other cases quoted above; they provide the info.
Simply put there is a judgement (which is what judjes do!) to make on the Port vs Stb as to when the port boat is committed to an action and cannot reasonable keep clear. Thus the speed and manoverability of the boats make a difference.
I always find taking these examples to the extreame always help to define them.
Consider 2 lasers, these are very slow, very manoverable boats; you might argue that a couple of boat lengths is enough. Consider two ORMA 60's sailed single handed, very fast and not very manoverable. You might suggest 500m in a big wind was the commitment point.
As for the RC's error in not putting a spacer mark in. It helps to prevent these situations, but if it is windy, the Stb boat with the kite up will still be sailing down into the port boats tracks. If the sailing instructions say that there is no spaces, the competitors
should be aware that this situation may occur and plan for it.
