Around that time the Oxford Psalter came out with pointing which tended towards a shorter reciting note and more syllables on the later notes in each part. Use of such pointing might make some discords uncomfortable if they needed to be repeated a couple of times.
Well, it's a theory, anyway.
Thank you very much! I thought that your book would have to be the earlier one. That presumably makes the weaker, OUP version a later revision - which I find very curious. There are actually at least four different versions of that last quarter in circulation, although whether they were all made by Ley I don't know. To my mind the strongest is Ley's first thought with the II7b for the antepunultimate chord.
Well, my copy is in his manuscript, presumably from sometime well before the end of his tenure at Ch Ch (1909-1926)*; it doesn't have the other changes you mention either.
* Edit: Inside the front cover he dates the book as "compiled in 1910 & revised in August 1923". The revision was the addition of a few alternative chants on spare lines, and in a couple of places a whole sheet of newly written out chants for a service glued over the old. On reflection, the change in writing style (specifically of the capital letter B ) means that my comment above about "another hand" was wrong, and the change I first remarked on was his (but either later or undecided, as it's in pencil).