Your confusion is that neither EF or AW have the run through Zion Narrows listed. I have hiked it in September. From Chamberlain's Ranch to the Temple of Sinawava is III. Looks like the higher rated section (Zions Park
) puts in at the takeout for the Narrows. There is the one 15'er the you can portage on the left.
Hope that helps. I'm hoping to get on it pretty soon myself.