Which, of course is wrong: the moon's cycle takes twenty-nine and a half days from New Moon to New Moon (or indeed to repeat any point, whether Full Moon, three-days-past-full gibbous, or whatever).
I shd know better -- after all, I have one of those beautiful moonphase poster calendars hanging on the stairwell -- but if anything slipped by me I'm not surprised it was in this section, which was by far the hardest part to edit of the entire project, and not just for its illegibility. To see Tolkien's mind go round and round over the same points without being able either to resolve the contradictions or be willing to abandon a hopeless project (since they cd only be fixed by altering one or more of the "fixed dates") was bad enough, but editing it required me to get into the same frame of mind to try to follow his line of thinking, which led to a lot of near-sleepless nights those two weeks I was working on this section.
Unfortunately, I forgot to ask Kristine for the specific page numbers where my gaff occurred -- one I've located (page 828, Text Note 2), where I shd have followed up with a correction mentioning the actual length needed. I'll make an update to this post when I find the other.
Still, at least I'm only repeating Tolkien's mistake, rather than taking something Tolkien had right and changing it to be wrong, which would have been embarrassing. The King of Gaffs in the book remains my passing reference to Gower as the author of PIERS PLOWMAN, wh. is as bad as referring to "Shakespeare's DOCTOR FAUSTUS" wd have been.