Passing on the hail is for the case where the hailed boat needs to tack (in order to give the hailing boat room) but needs room from a third boat in order to do so.

As I read the original post, that is not the situation described. In this scenerio, the hailed boat is able to give room without passing on the hail, but the original hailing boat needs room from one or more additional boats.

Imagine, for example, a line of starboard-tack boats bow-to-stern on the layline to clear the end of a jetty (boats A, B, C, D, etc.). Just below the layline is another starboard-tack boat (boat Z). Z needs to tack to safely avoid the obstruction. She hails the boat beside her (A) for room. A can tack away without needing extra room from B. Therefore, A tacks without passing on Z's hail. There is not, however, enough room for Z to tack and cross B, nor enough room for her to tack and duck below B, C, D, etc. either.

In that instance, I believe Z could hail B for room to tack as well as A.

Perhaps I'm reading too much into the first question though. If instead of being bow-to-stern, the line of boats (A to D) were overlapped, then Z would hail A under rule 20.1. A would pass the hail on to B under rule 20.3. B would pass the hail on to C etc.

Regards,
Eric