" A good crew on L will not let W in there, but the only legal way to keep W out is to luff with enough time such that W can't get overlapped with the stern of the signal boat. If that happens, L has allowed W space to which W was not entitled, but at that point has no recourse (especially not luffing W into the signal boat)."

From Mike's post... I was unaware that overlap to the Signal Boat. I thought it was overlap on the clear ahead boat..

So if the signal boat is longer than the boats sailing, an overlap could be established by W if they cross the stern of the signal boat, even before they reach the stern of L?