In my previous hypothetical example of boats approaching a leeward mark, the windward boat (Yellow) broke overlap by means of a lucky puff. So, what can Yellow do to protect her position if she isn't so lucky?

I've redrawn the diagram to answer that question:



Again, prior to position 1, the boats are overlapped on the same tack more than two hull-lengths apart. Therefore Blue is not restricted by RRS 17.

At position 2, Yellow turns up sharply enough to break the overlap with Blue. She then turns back down.

At position 3, overlap is reestablished, with Blue coming from clear astern within two hull-lengths. Now RRS 17 does apply. Blue may not sail above her proper course. Blue must turn down to sail towards the mark, which she does by position 4.

This maneuver by Yellow is known as a "Tactical Luff". Most rules authors diagram it between boats on a beat to windward, but I think catamarans are more likely to use the tactic going downwind as I've drawn.

I hope that helps,
Eric